ward off wastewater woes - chemical processing

Ward Off Wastewater

Woes

Wastewater eHANDBOOK

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TABLE OF CONTENTSUnderstand Industrial Wastewater Treatment 7A variety of techniques play roles in removing contamination

Adroitly Address Wastewater Challenges 14Focus on six key compliance and water consumption issues

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Process plants generally try to min-

imize the amount of wastewater

they generate. However, operations

invariably result in production of some

wastewater. Proper treatment of this waste-

water is crucial for both environmental and

economic reasons.

Industrial wastewaters usually contain

organic and inorganic matter in varying

degrees of concentration. They may include

toxic and other harmful materials as well as

components that are non-biodegradable

or that can reduce the efficiency of many

wastewater-treatment operations.

Thus, treatment of industrial wastewaters

typically is a very difficult task — far more

complicated than municipal wastewater

treatment — that requires special methods

and sophisticated technologies. These

options fall into three categories: physical,

chemical and biological. Physical treatment

methods include sedimentation, flotation,

filtering, stripping, ion exchange, adsorption

and other processes that remove dissolved

and non-dissolved substances without nec-

essarily changing their chemical structures.

Chemical methods include chemical pre-

cipitation, chemical oxidation or reduction,

formation of an insoluble gas followed by

stripping, and other chemical reactions

that involve exchanging or sharing elec-

trons between atoms. Biological methods

rely upon living organisms using organic

or, in some instances, inorganic substances

for food.

Biological treatment is more widely used

than any other option where reasonably

Understand Industrial Wastewater TreatmentA variety of techniques play roles in removing contamination

By Amin Almasi, mechanical consultant



complete treatment is required. It most

often serves as the secondary treatment

stage to remove major portions of contami-

nation. Other processes handle primary and

tertiary treatment to complete the removal

of solids and other pollutants.

THE CHALLENGESome industrial wastewaters are rich in

organics and easily biodegradable while

others are nutrient deficient, inhibiting or

preventing biodegradability. Total dissolved

solids and contamination may exceed by

many times the levels found in domestic

sewage. Industrial wastewaters often also

have pHs well beyond the range of 6–9 and

may contain high concentrations of dis-

solved metal salts. To further complicate

matters, wastewater flows and charac-

teristics within a plant also can vary with

time because of campaign manufacturing

or slug discharges on top of the usual dis-

charges. In addition, spillages and dumping

that occasionally may occur very adversely

can impact the performance of the plant’s

wastewater treatment plant. Consequently,

it’s always prudent to carefully assess

current wastewater and its treatment

requirements rather than relying on the past

situation. An understanding of the nature of

the plant’s operations is vital.

One key parameter for wastewater is its

biochemical (or biological) oxygen demand

(BOD). This is the amount of dissolved

oxygen needed by aerobic biological

organisms to break down organic mate-

rial present in a given wastewater sample

at a certain temperature over a specific

time period. Therefore, BOD indicates indi-

rectly the amount of organic compounds

in wastewater. The BOD most commonly

is expressed in milligrams of oxygen con-

sumed per liter of sample during 5 days of

incubation at 20°C.

Another key parameter is chemical oxygen

demand (COD), which indirectly specifies

the amount of organic compounds in the

wastewater. It indicates oxygen consump-

tion and also is given in mg/L.

Both BOD and COD measure the amount

of organic compounds in wastewater.

However, COD is less specific because it

measures everything that can be chemically

oxidized rather than just levels of biode-

gradable organic matter. You can estimate

the biodegradability of wastewater by con-

sidering its COD and corresponding BOD.

PRIMARY TREATMENTRemoving large, suspended and float-

ing solids is the focus of the first stage of

wastewater treatment. However, before

such treatment takes place, the plant

wastewaters usually first go to an equaliza-

tion tank or system, which acts as a buffer

and normalizes varying flow and contami-

nation loads. It’s always best to use a single

large concrete tank to which an appro-

priate coating has been applied. This tank



most often is sized based on the difference

between expected peak and average flows,

with a capacity of 4–8 hours’ worth of dif-

ference common.

From the equalization tank, the raw

wastewater goes for primary treatment.

This usually includes screening to trap

solid objects, sedimentation by gravity

to remove suspended solids and some

adjustments. Primary treatment sometimes

is referred to as “mechanical treatment”

because it relies on mechanical meth-

ods, although chemicals often are used

to accelerate the sedimentation process.

The design for a primary treatment facility

most often includes neutralization (i.e., pH

adjustment), coagulation, flocculation and

dissolved air flotation (DAF).

The main purpose of primary treatment is

to remove colloidal solids, emulsified oil and

a small portion of BOD and COD. Primary

treatment can reduce BOD of the incom-

ing industrial wastewater by around 20–30

% and the total suspended solids by some

50–65%.

Neutralization. Usually, wastewater must

have its pH adjusted so that subsequent

operations such as downstream biological

treatment can take place at optimum pH.

Therefore, the wastewater passes to a neu-

tralization system that corrects its pH. This

system generally involves multiple neutral-

ization tanks; common configurations are

“3+1” (3 operating + 1 standby), “5+1” (5

operating + 1 standby) and “7+1” (7 operat-

ing + 1 standby). Injection of chemicals such

as a caustic soda or sulfuric acid solution

adjusts the pH to the desired level.

Sensors installed at the inlet and outlet of

the neutralization tank (a minimum of one

sensor in each location) measure the pH

of the wastewater. A controller uses these

readings to automatically adjust a dosing

pump to achieve the desired final pH (typi-

cally, 6.7–8.3 with an optimum of 6.9–7.4).

The neutralization-chemical system con-

sists of storage and mixing tanks and other

equipment such as agitators necessary to

reduce the concentration of the chemical

and prepare it for injection. Dosing pumps

are deployed in a “1+1” arrangement (1 oper-

ating + 1 standby) for each chemical. Often

positive displacement pumps handle these

services. However, these sometimes can

pose maintenance and reliability issues. A

variable-speed-drive centrifugal pump often

offers an attractive alternative that provides

reliability and high performance.

Coagulation and flocculation. Wastewater

from the neutralization tank usually flows by

gravity into coagulation tanks for removal

of colloidal solids. Coagulation is a quick

process, requiring a relatively low retention

time of 2–5 min. There commonly are mul-

tiple rectangular coagulation tanks made

of reinforced concrete with proper coating;



each contains a few agitators that provide

high-energy mixing. Large plants often use

configurations such as “7+1” (7 operating + 1

standby) or “9+1” (9 operating + 1 standby)

or similar. For instance, a treatment plant of

3,000-m3/hr total capacity employed “7+1”

tanks, each of 16 m3 capacity, to achieve

retention time of more than 2.2 minutes.

Some large plants have used retention

times as low as 1.5 min and certain radical

designs propose times as low as 1 min. How-

ever, low retention times can pose risks.

Generally, it’s wise to keep retention times

above 2 min.

A coagulant solution (typically polymer

based) usually is injected automatically

by dosing pumps (“1+1” configuration);

most often stroke variation adjusts injec-

tion. Modern plants automatically control

injection rate according to incoming

flow rate based on a more or less fixed

chemical concentration, preliminarily

defined through site experimental tests

and adjustable during normal plant oper-

ation. Coagulant aid can be added to the

wastewater stream to facilitate separation

of solids.

Wastewater from coagulation tanks most

often flows by gravity into the floccula-

tion system (tanks) where agglomeration

of flocculent formed during coagulation

process takes place. Anionic polymer usu-

ally serves as flocculent. Flocculation is

a process of slow mixing with retention

times of 12–40 min. Some designs for large

plants have used lower retention times,

say, 9–10 minutes, but typically times of 11,

12 or 15 min. are recommended. It is a pro-

cess that requires less energy for agitation

than coagulation.

Dissolved air flotation. Wastewater from

flocculation passes by gravity into a DAF

clarifier system. Its main purpose is to

remove the suspended solids, emulsified

oil, grease and some portions of BOD and

COD from the wastewater. Elimination

occurs through the action of micron-sized

air bubbles. These are created by dissolv-

ing air in wastewater under pressure and

then reverting to atmospheric pressure in

DAF clarifiers. The millions of micron-size

air bubbles released attach to the contam-

inants, decreasing their effective density

and thus causing them to float on the sur-

face to form a concentrated sludge blanket.

A skimming device removes the floating

sludge, which then go to sludge treatment

units for processing. A common design uses

a separate pressure vessel for compressed

air introduction. DAF clarifiers operate

effectively over a wide range of hydraulic

and contamination loading.

SECONDARY TREATMENTOften considered the heart of the treatment

plant, its major purpose is to remove biode-

gradable organics (expressed as BOD, COD,

etc.) and ammonia. Secondary (or biolog-

ical) treatment uses microbes to consume



dissolved organic matter that escapes pri-

mary treatment, converting it to carbon

dioxide, water and energy for microbe

growth and reproduction. After this biolog-

ical process, the stream goes to additional

settling tanks (“secondary” clarifiers or sed-

imentation vessels) to eliminate more of the

suspended solids. Well designed and func-

tioning secondary treatment can remove

about 85–90% of the suspended solids and

BOD. Technologies employed include the

activated sludge process, which is the most

commonly used method, as well as variants

of pond and constructed wetland systems,

trickling filters and other forms of treatment

that rely on biological activity to break

down organic matter.

An activated-sludge train usually is divided

into an aeration section for BOD removal

and nitrification, and an anoxic section for

denitrification. In the aeration section, com-

pressed air passes through the wastewater.

Dissolved oxygen from the compressed

air acts as a respiratory source for aerobic

bacteria present in wastewater that decom-

pose the organic load (expressed as BOD

and COD) and ammonia to carbon dioxide

and nitrates, respectively. In the anoxic sec-

tion, bacteria use the oxygen in nitrates as

a respiratory source, thus converting the

nitrates to nitrogen gas.

In practice, denitrified wastewater from

the anoxic tank flows downstream to the

aeration (or BOD-removal) tank where

aerobic bacteria decompose the organic

load and ammonia present using dissolved

oxygen supplied by air blower(s). The

treated effluent from the aeration tank

usually flows by gravity to a secondary

clarifier, which most often is a gravity

clarifier. Here, sludge is removed from

the treated effluent, which then passes

to tertiary treatment. A portion of the

sludge gets recycled to the anoxic sec-

tion to provide nitrates for denitrification.

This recirculation keeps effluent nitrates’

concentration below the required limits.

The remaining portion of sludge goes to

sludge treatment facilities.

Biological treatment usually consists of

multiple streams, say, 4, 6 or 8 trains, with

a proper safety factor (for instance, 1.5 or

more) to ensure the biological treatment can

handle the incoming design flow even if one

train is taken out of operation. Selection of

the hydraulic retention time for the anoxic

zone requires great care. Considering dif-

ferent operational and process factors, as

a rough indication, this time usually is 5–8

hr. Some designs for large plants have used

5.5 hr, 6 hr and 6.5 hr as optimum values.

Hydraulic retention time for the aeration

Selection of the hydraulic retention time for the anoxic zone requires great care.



tank is longer, somewhere between 19 and

24 hr. Some large plants have found a reten-

tion time of 20 hr to be optimum.

TERTIARY TREATMENTThis ensures removal of remaining contam-

ination and solids in the wastewater. Such

tertiary treatment usually involves filtration

systems such as disc filters, reverse osmosis

(RO) units (Figure 1), etc. You usually should

direct filter reject from backwash or RO

unit rejects to the flow distribution cham-

ber upstream of the equalization system;

most often, these rejects require a dedicated

pumping system. To eliminate specific con-

taminations to meet regulatory requirements,

many plants must resort to special treatment,

e.g., the Fenton process to remove non-bio-

degradable COD. While other technology

options are available, the Fenton process

most often is selected because of its reliabil-

ity, initial cost, operational cost and footprint.

The Fenton section usually consists of

dosing systems for hydrogen peroxide

and ferrous sulfate. After dosing with

chemical in an oxidation tank, the waste-

water goes to tube settlers to settle out

the contaminants. During regular oper-

ation plants generally don’t need to put

wastewater through such treatment. How-

ever, having a Fenton section can ensure

treatment adequacy when facing sus-

tained peak COD in the wastewater.

Many units in tertiary treatment such as

that for the Fenton process or fine filtra-

tion should consist of multiple parallel

streams to provide flexibility during oper-

ation. Commonly used arrangements are

“n+1” and “n+2” — for example, “2+2” “3+1”

“4+2” and “5+1”.

AMIN ALMASI is a mechanical consultant based in

Sydney, Australia. Email him at [email protected].

REVERSE OSMOSIS

Figure 1. Use of such a unit for tertiary

treatment of wastewater is

becoming popular.



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Wastewater management is one

of the most challenging oper-

ational issues facing chemical,

petrochemical and other process plants

today. Three primary factors contribute to

this: wastewater compliance standards are

growing increasingly strict, water consump-

tion costs are rising, and a water shortage is

looming in many areas.

The U.S. Environmental Protection Agency

(EPA) assessed a staggering $69 million in

pollution penalties in 2018 alone. Meanwhile,

the cost of water is getting higher through-

out the United States. In addition, more

and more processors are treating effective

and efficient processing of fluid byprod-

ucts as much as a corporate sustainability

imperative as an environmental responsibil-

ity. This is a pressing issue for all chemical

processing operations but smaller facilities

may feel improved wastewater manage-

ment is out of reach because they lack

in-house compliance expertise or advanced

wastewater-treatment technologies. What’s

more, understanding a facility’s wastewa-

ter compliance obligations can be difficult

because dense regulatory terminology per-

meate wastewater standards and mandates

may depend upon the particular local pub-

licly owned treatment works (POTW).

Chemical processors that take steps to

better understand wastewater regula-

tions and deploy advanced technologies

to reduce recurring costs associated with

wastewater compliance will position them-

selves for a stronger future. Here are six

areas to focus on to take control of waste-

water compliance.

Adroitly Address Wastewater ChallengesFocus on six key compliance and water consumption issues

By Tim Hanna, PRAB



1. CRITERIA BEHIND REGULATIONS Wastewater discharge regulations include

a fair amount of complexity. Lack of a

high-level understanding of their frame-

work and enforcement can pose a real

barrier to effective and efficient compli-

ance management.

Since 1972, the United States has pursued an

increasingly stringent water control program.

From the EPA’s perspective, two kinds of

wastewater discharges need to be regulated

under the Clean Water Act (CWA): direct

discharges into “waters of the United States”

and indirect discharges that pass through a

POTW for treatment prior to being released

into the water supply.

Indirect discharges are regulated through

a national pretreatment program that is

a cooperative effort of federal, state and

local environmental regulatory agencies.

The objective of the program is to pro-

tect POTWs’ infrastructure and reduce the

amount of industrially generated pollutants

discharged into the municipal sewer system

and the environment.

The EPA has established three primary

kinds of pretreatment standards:

• general and specific prohibited discharge

standards for all industrial users;

• categorical pretreatment standards for

particular industrial categories, including

inorganic chemicals, ink formulating, oil

and gas extraction, organic chemicals,

plastics and synthetic fibers, paint for-

mulating, pesticide chemicals, petroleum

refining, pharmaceutical manufacturing,

rubber manufacturing, and soap and

detergent manufacturing; and

• local limits that are site-specific to ensure

the POTW will not process waste that

passes through to the water supply or

interferes with operations.

Standards outside of the CWA also factor into

wastewater compliance. Under the Resource

Conservation and Recovery Act (RCRA), the

EPA regulates the transport, treatment, stor-

age and disposal of solid waste (including oils

and sludges). While not a direct component

of discharge regulations, U.S. Occupational

Safety and Health Administration (OSHA)

standards also impact a chemical processor’s

approach to wastewater management. Toxic

and other hazardous gases can arise when

certain inorganic pollutants in wastewater mix

in the discharge collection system. OSHA sets

exposure limits on toxic and air contaminants

to protect worker health. POTWs will reduce

this risk by controlling the maximum level of

pollutants discharged.

Tip: When it comes to understanding the

scope of wastewater requirements for a

plant — and optimizing solutions to manage

wastewater treatment — operators must

appreciate that air discharge limits also play

a role. For example, a wastewater treatment

system requires proper ventilation. If a wet

scrubber removes toxic substances from



gases, the toxic substances will collect in

the wastewater generated by the scrubber,

creating an additional wastewater stream to

manage.

2. THE PURPOSES OF PERMITTINGAt a minimum, the EPA requires all signifi-

cant industrial users (SIUs) to have permits.

The EPA defines SIUs as:

• industrial users (IUs) that fall under cat-

egorical pretreatment standards due to

their industry;

• IUs that discharge an average of 25,000

gal/d or more of process wastewater

(excluding sanitary, noncontact cooling

and boiler blowdown wastewater) to

the POTW;

• IUs that contribute a process waste

stream that makes up 5% or more of the

average dry-weather hydraulic or organic

capacity of the POTW;

• IUs that the control authority identifies as

having a reasonable potential to adversely

affect the POTW’s operation; and

• IUs that have violated any pretreatment

standard or requirement.

The permitting process usually is one of the

clearest illustrations that the onus of pro-

active wastewater compliance falls on the

process plant. Not only can local wastewater

authorities define SIUs in their jurisdiction

more stringently than the federal EPA but

also EPA counsels local wastewater authori-

ties to communicate pretreatment standards

during the permitting process. In “The

Industrial User Permitting Guidance Manual,”

https://bit.ly/3k8fpg1, the EPA states that, in

its experience, “the permit is the most effec-

tive means of ensuring that industrial users

are aware of all applicable pretreatment

requirements.”

Most permit applications require plants

to disclose a broad range of details about

their wastewater management, such as a

description of operations, wastewater gen-

erating and discharge activities, and the

pollutants potentially in the wastewater

and on-site. From the chemical proces-

sor’s perspective, it would seem that the

operator must supply all the details of its

wastewater management practices prior

to learning which discharge regulations

will apply. This approach compromises

the operator’s ability to initiate pollution

abatement practices that may streamline

permit approvals and reduce surcharges

levied by the POTW to cover costs for

treating wastewater with excessive pollu-

tion levels.

Tip: For plants that add an in-house

wastewater treatment system, the permit

application will need to clearly state where

the system will be located within the facility

and the location of the sample port so reg-

ulators can perform testing. Some suppliers

of wastewater treatment technology will

work with plants and wastewater regulators

to submit and obtain the necessary permits

on behalf of the facility.



3. RECURRING COMPLIANCE COSTS Wastewater compliance can incur many

costs such as treatment expenses, labor

investments, and fines that can erode a

chemical processor’s bottom line.

Wastewater compliance lapses, for example,

can lead to serious financial liability. A facil-

ity negligently or knowingly discharging to a

POTW in violation of federal or local pretreat-

ment standards can face significant penalties:

• negligence violations — initial penalty:

1 year and/or $2,500–$25,000/d, sub-

sequent convictions: 2 years and/or

$50,000/d; and

• knowing violations — initial penalty: 3

years and/or $5,000–$50,000/d, sub-

sequent convictions: 6 years and/or

$100,000/d.

If a discharge introduces a pollutant or haz-

ardous substance into a POTW and the

person knew or reasonably should have

known such pollutant could result in injury or

damage the system, or the discharge causes

the plant to violate its own permit, the penal-

ties are the same as those for a discharge to

a POTW in violation of a local pre-treatment

program.

Chemical processors have two choices if

they are to avoid such compliance fines:

treat wastewater to meet local POTW stan-

dards prior to discharging it to the sewer

or pay to have wastewater hauled away

and treated, which easily can total several

thousand dollars per week. The costs to

transport (either by bulk drums or tank-

ers) and treat wastewater are increasing

and likely will continue trending upward.

According to data from the U.S. Bureau of

Labor Statistics, costs for waste collection

and remediation services rose 12% from

June 2014 to June 2019.

Tip: Facilities that have an in-house waste-

water treatment system and a discharge

permit are not exempt from monitoring

and testing. These plants still must perform

regular visual tests and send samples out

for an official analysis (usually twice a year).

Additionally, failure to pay fees, charges or

surcharges typically are viewed as compli-

ance lapses and also are subject to legal

action.

4. WATER USE COSTS While wastewater compliance is a neces-

sary aspect of chemical manufacturing,

reducing water consumption expenses is a

related component of cost-effective waste-

water management.

According to estimates in 2017 research

from the American Council for an Ener-

gy-Efficient Economy, www.aceee.org,

among all U.S. manufacturing sectors,

chemical making accounted for the third

greatest volume of water withdrawal,

behind only pulp and paper and pri-

mary metals. More important, though,

the chemicals subsector ranked highest



in consumptive use, followed by primary

metals and petroleum refining.

With water costs rising and water demand

expected to exceed the current supply by

2030, taking steps to reduce water con-

sumption through wastewater recycling and

re-use could dramatically impact chemical

processing facilities for the better.

Tip: Recycling or repurposing washdown

water can cut water consumption substan-

tially. For example, a chemical blender of

industrial metalworking fluids uses as much

as 20% of its incoming water to clean out

the facility’s mixing vats. Treating this water

enables its reuse, markedly reducing incom-

ing water usage.

5. OUTSIDE EXPERTISE Achieving wastewater compliance in a

cost-effective manner requires a balance of

technology and compliance expertise. An

ability to work with local control authorities

to become familiar with applicable regu-

lations and adopt measures to meet the

regulations underpins this.

Unfortunately, chemical companies —

whether new or long-established — can find

pursuing pre-emptive compliance measures

extremely challenging when their primary

information liaison is also the enforcing party.

An experienced, trusted supplier of industrial

wastewater treatment technology will be

familiar with local and federal pre-treatment

standards and, in some cases, can act as an

“information agent.” For example, when a

plant operator poses questions to wastewa-

ter regulatory officials, it may risk inviting

followup requests from the regulator. As a

neutral third party, a wastewater equipment

supplier may be able to answer the questions

itself or consult with regulators without dis-

closing specific details.

Furthermore, wastewater treatment

systems for chemical plants are not

one-size-fits-all. Determining the most

cost-efficient and effective technology for

the specific application requires a thorough

understanding of the wastewater’s makeup

(Figure 1). For example, correctly specifying

and optimizing a reverse osmosis system

demands the following data: pH, total dis-

solved solids, chemical oxygen demand,

biochemical oxygen demand, operating

temperature, chloride, ammonia, oil and

THOROUGH EVALUATIONFigure 1. Selecting the most appropriate treat-ment system requires a detailed and accurate analysis of the wastewater.



grease, total suspended solids, sulfates,

calcium, magnesium, and emulsified oil and

grease.

Tip: Do not exclusively rely on historical

wastewater data. Carefully evaluate the

current wastewater in the context of the

plant’s current operating parameters, which

are subject to change as production goals

fluctuate. An experienced and trusted sup-

plier of industrial wastewater technology

can evaluate a facility’s wastewater stream

by running tests and obtaining a laboratory

analysis of samples before and after various

treatment options. From those results, the

supplier can recommend the proper equip-

ment and treatment methods to recycle or

repurpose the permeate.

6. ZERO-LIQUID-DISCHARGE TECHNOLOGIES The EPA’s Effluent Guidelines, www.epa.

gov/eg, set technology-based numerical

limitations for specific pollutants on an

industry-by-industry basis, including sev-

eral chemical processing applications. The

guidelines don’t require the use of a specific

technology to achieve reduction.

Several available zero-liquid-discharge

technologies can be installed on-site to

cut water pollution and prepare water for

repurposing within the production facil-

ity. In many instances, a plant may need

to deploy multiple modular technologies

to optimize wastewater treatment and

recycling. Three of the most common

processes for chemical plant wastewater

treatment are ultrafiltration, vacuum evapo-

ration and reverse osmosis.

• Ultrafiltration uses low pressure to push

wastewater through a semipermeable

membrane. The technology filters out

organics, emulsified oils and suspended

solids, reducing oily water volumes by as

much as 98% without chemicals. Ultra-

filtration systems can cut the cost of

washwater and detergents by as much

as 75% and decrease haul-away costs by

90%. Such systems can help manufactur-

ing facilities meet a goal not hauling away

any wastewater and provide them the

ability to meet RCRA requirements and

state and local discharge regulations.

• Vacuum evaporation is one of the most

effective methods for mitigating the

risks and costs associated with chemical

manufacturing wastewater. This process

removes salts, heavy metals and a vari-

ety of hazardous components. It restores

90–95% of the original distillate (water),

cuts the cost of washwater and deter-

gents up to 75%, and reduces water costs

up to 99%. Vacuum evaporation also has a

low carbon footprint.

• Reverse osmosis is a low-maintenance

method that removes dissolved solids by

using high pressure to push wastewater

through a semipermeable membrane.



The technology removes up to 99.5% of

dissolved salts and impurities. Often this

technology serves as the final process

after ultrafiltration or chemical treatment

of wastewater.

Tip: Partner with a wastewater treatment

system supplier that offers all types of

technology and that will work in lockstep

with plant operators throughout the entire

equipment acquisition — from sampling

and permitting to testing and installation.

Also, be sure to pursue testing and feasi-

bility studies before equipment selection.

Equipment suppliers that collect waste-

water samples from the plant, run those

samples through their proprietary waste-

water treatment systems and then verify

the results of the processing through a

certified laboratory not only have proof of

projected water quality improvements but

also will have collected data required for a

new discharge permit application.

BUOY YOUR BOTTOM LINEWastewater regulations almost will

certainly grow increasingly stringent.

Chemical processors that partner with

wastewater treatment experts to establish

improved compliance practices will bene-

fit from lower discharge fees, labor costs

and haul-away expenses. In addition, by

recycling wastewater to the production

line for use, a plant will lower fresh water

expenses. Chemical manufacturers that

leverage this potential will make waste-

water compliance less of a drain on their

operation.

TIM HANNA is the vice president of business devel-

opment for PRAB, Kalamazoo, Mich. Email him at

[email protected]

REVERSE OSMOSIS UNITFigure 2. This technology can remove up to 99.5% of dissolved salts and impurities, and often serves as the final step in a treatment system.



http://myronl.com

The varying compositions of chem-

icals we use today are as diverse

as the manufacturers and the dis-

tributers who ensure a steady supply for

consumers and industry alike. Likewise, the

technology these companies use to mea-

sure and manage their chemical inventories

can be just as diverse.

These facilities have an array of options

for measuring the amount of chemi-

cals they have inside their tanks. A large

chemical manufacturer and distributor

had previously been using weigh scales

installed beneath every tank and vessel at

its facility in Illinois. However, it recently

switched to high-frequency through-

air radar sensors. This article compares

the two technologies and highlights the

their differences.

WEIGH SCALES Weigh scales, sometimes referred to as

load cells, are in wide use for measuring

inventory in large tanks. These scales are

installed under a chemical tank to make

a weight measurement. Using this mea-

surement and a known density, the sensor

electronics can output a volume to help

facilities better manage their inventory.

Weigh scale technology is easy to under-

stand, and it works. A weight measurement

is made mechanically, which can be cal-

culated easily into an accurate volume

measurement using a known density and

a simple formula. Because weigh scales

have no contact with the medium being

measured, these sensors can measure any

liquid chemical despite corrosive or harm-

ful properties.

Measurement Methods for Chemicals Inventory Abound Illinois facility finds success with radar sensor technologyBy Greg Tischler, VEGA Americas



The straightforward measurement,

however, is where the simplicity ends.

Installations alone can be costly, time-con-

suming and labor-intensive. Installing a

single system means lifting the entire

vessel and placing the weigh scale under-

neath. Shutting down a process or taking

a vessel out of use, if necessary, increases

costs further.

Weigh scales also are expensive to main-

tain. These instruments make a mechanical

measurement, so they need to be cleaned

regularly, recalibrated and repaired. All of

this takes valuable time for maintenance

crews, and yet, for many facilities, this

process has become routine. Every few

months, vessels are taken out of service so

maintenance crews can inspect and reca-

librate instrumentation. They don’t realize

there’s another way.

HIGH-FREQUENCY RADARThrough-air radar works by emitting

radio microwaves from the radar antenna

system to the measured product where

it is reflected by the product surface and

back to the antenna system. The radar

sensor uses time of flight to measure

product level. Radar sensor electronics

can use the level measurement and the

vessel geometry to calculate product

volume inside the tank.

Real-world benefits of high frequency

80 GHz radar can be seen in an array of

applications, including chemical tanks.

Radar sensors with 80 GHz frequency have

enhanced focusing, the ability to make

measurements through plastic vessels and

special software to generate an accurate

and reliable echo curve to interpret the

level inside the vessel.

A radar beam’s focus is dependent on two

factors: the radar transmitter’s antenna size

and its transmission frequency. A smaller

antenna or a lower frequency results in

a wider, less focused beam. Conversely,

a larger antenna or a higher frequency

results in a narrower, more focused signal.

Therefore, a radar sensor using a high 80

GHz frequency can accurately measure

in small or narrow vessels with little to

no interference.

Radar signals also can also penetrate non-

conductive products such as plastic and

fiberglass. Because many chemicals are

stored in tanks made of polyethylene,

Installation alone can be costly, time-consuming and labor-intensive.



commonly referred to as poly tanks, an 80

GHz radar sensor can be installed above

these tanks without the need for an addi-

tional process connection (Figure 1). This

simplifies and decreases the costs associ-

ated with installation.

The intelligent electronics within today’s 80

GHz radar sensors multitask to meet indi-

vidual user needs. In its most basic function,

the electronics output a level measurement,

but it also can calculate a volume measure-

ment using known vessel geometries. Those

same electronics even can filter out signal

interference from condensation or dust and

dirt built up on the antenna, eliminating

the need for regular maintenance, cleaning

or recalibrations.

MEASUREMENT TECHNOLOGY UPGRADEThe chemical manufacturer and distribu-

tor in Illinois had grown tired of calibrating

its weigh scales constantly. Tanks at this

facility ranged in size from small, portable

tanks to large vessels capable of holding

thousands of gallons. Over time, measure-

ments would drift, which resulted in slight

measurement errors at best and dangerous,

costly spills at worst. And whenever the

facility needed to move a tank, the weigh

scale sensors would have to be recalibrated

and recertified. The cost of maintaining all

the weigh scales was growing.

After exploring the available measurement

options, operators at the facility chose

RADAR SENSOR ABOVE POLY TANKFigure 1. The radar sensor is mounted above the polypropylene tank, eliminating the need for an additional process connection.



to purchase an 80 GHz radar sensor with

a fixed cable connection attached to a

chemical-resistant polyvinylidene fluoride

(PVDF) housing. Installation was inexpen-

sive and straightforward. Maintenance

installed some of the radars in existing

process connections on top tanks, while

others simply hung the radar above the

poly tank and measured through the top

of the vessel.

ACCURATE RESULTS WITH LESS MAINTENANCEInstalling these radar sensors resulted in

accurate measurements, which eliminated

inventory errors, overfilling and safety

concerns related to incorrect measure-

ments. The sensors provided accurate

volumetric measurement outputs with-

out the need for ongoing maintenance. A

simple swap of measurement instrumen-

tation improved operational efficiency

and safety records. Now the company is

moving forward with plans to standardize

its measurement instrumentation at facili-

ties across the United States.

GREG TISCHLER is radar and guided wave product

manager at VEGA Americas. He can be reached at

[email protected].

RADAR SENSOR AND DISPLAY INSTRUMENTFigure 2. The VEGAPULS C 11 radar sensor hangs above the chemical tank and provides an accurate level measurement, which is shown on the VEGADIS 81 display instrument next to the vessel.



http://info.tuthill.com/chemicalprocessing

Sewage treatment is more than a dirty

job. It is considered a hazardous

work environment by the U.S. Occu-

pational Safety and Health Administration

(OSHA); the U.S. Environmental Protection

Agency (EPA); the National Fire Protection

Association (NFPA); as well as multiple other

local, state and global regulators.

Employees working in wastewater treat-

ment plants from face real dangers,

including exposure to combustible and

toxic gases such as hydrogen sulfide (H2S),

methane (CH4), carbon monoxide (CO) and

others, as well as hazards associated with

oxygen (O2) deficiency in confined spaces.

Pumps stations supporting the primary

phase of the wastewater treatment process

(Figure 1) are a recognized area of concern

for gas safety. Inflows from municipal sewer

lines are directed to large, open-air tanks

before treatment. Fixed gas detector mon-

itoring of dry and wet wells is necessary

to avoid dangerous combustible and toxic

levels of these naturally occurring waste

gases.

As a recognized industry safety standard

with the de facto force of regulation, com-

pliance with NFPA Code 820 Standard for

Fire Protection in Wastewater Treatment

and Collection Facilities is designed to

prevent gas explosions and fires. Other

industry standards that apply include IEC

61508 and 61511, which help ensure the safe,

dependable and reliable design and opera-

tion of combustible gas and flame detection

monitoring equipment and systems across a

range of industrial applications.

Integrated Gas Monitoring Systems Help Meet NFPA Code 820Keep workers and physical assets safe from hazardsBy Tim Wolk, MSA Safety



Wet wells are the large, open holding tanks

where municipal wastewater is stored ini-

tially at treatment plants. In these large

tanks, heavier solids sink to the bottom and

lighter materials float to the top for removal

before the remaining wastewater is pumped

to secondary treatment areas. During

this process, mixed levels of combustible

and toxic gases such as methane, hydro-

gen sulfide and other dangerous gases

can be present in varying quantities. Here

the potential for oxygen deprivation also

exists—especially in confined space areas.

The combustible gases and the toxic gases

generally are invisible and can exhibit a

rotten-egg smell (hydrogen sulfide) or

pungent smell (methane), which can be

deceiving in terms of their potentially lethal

nature—in terms of both combustibility and

toxicity. Combustible and toxic gas detec-

tors alert system operators when this gas

cocktail becomes intense enough to rep-

resent a serious fire danger or respiratory

threat to employees.

COMBUSTIBLE GASESCombustible hydrocarbon and toxic gases,

such as methane, are natural by-products

of human and animal waste streams. When

gathered and collected through municipal

sewer systems into large waste streams for

treatment, they become concentrated, often

leading to odor control issues and potentially

hazardous combustible gas levels affecting

worker safety. This can occur during rou-

tine maintenance activities requiring the use

of tools and other common equipment, in

WASTEWATER PUMP STATIONFigure 1. This di-agram portrays a typical wastewater treatment plant and process layout.



which mixed waste gases are highly com-

bustible under the right conditions at 100%

lower explosive limit (LEL).

HYDROGEN SULFIDEOnce released into the air, H2S gas with its

rotten egg smell can be present for weeks

as an annoying and potentially dangerous

air pollutant. While not technically a green-

house gas, it has been dubbed the “other

greenhouse gas” by some because it tends

to get trapped within the atmosphere.

According to the National Institute for

Occupational Health and Safety (NIOSH),

H2S exposure can cause irritation to the

eyes and respiratory system. At higher

levels, it results in apnea, coma, convulsions,

dizziness, headache, weakness, irritability,

insomnia and stomach upset, leading to

death in the worst cases.

CARBON MONOXIDECarbon monoxide is an odorless, colorless

gas that can cause sudden illness and death.

It is produced any time a fossil fuel is burned,

such as when excess waste gas is flared at

municipal waste treatment facilities or in con-

fined areas where gasoline-powered engines

are present. Exposure to CO impedes the

blood’s ability to carry oxygen to body tis-

sues and vital organs. Common symptoms

are headache, nausea, rapid breathing, weak-

ness, exhaustion, dizziness and confusion.

Severe exposure can result in damage to the

brain or heart—and even death.

OXYGEN DEFICIENCYOxygen-deficient atmospheres are the

leading cause of worker confined-space

fatalities in industrial plants in which

employees must perform routine main-

tenance tasks. While normal atmosphere

contains between 20.8 and 21% oxygen,

OSHA defines as oxygen-deficient any

atmosphere that contains less than 19.5%

oxygen and as oxygen enriched any atmo-

sphere that contains more than 22%.

Oxygen deficiency in municipal wastewater

treatment plants is a real threat to worker

safety with their complex array of large

tanks, vaults, pipes and other equipment.

NFPA CODE 820NFPA Code 820 has been around for

decades and has gone through multiple

iterations to improve its effectiveness. The

scope of this standard is to establish min-

imum requirements for protection against

fire and explosion hazards in wastewater

treatment plants and associated collection

systems, including the hazard classification

of specific areas and processes.

This important safety standard identifies

three separate process areas of concern

relating to combustible gases: (1) collec-

tion areas, (2) liquid streams and (3) solids

treatment. The standard applies to multiple

types of sewers, pumping stations, treat-

ment facilities, sludge handling facilities,

chemical handling facilities, treatment facili-

ties and ancillary structures.



The requirements for monitoring wet wells

with combustible gas detectors are identi-

fied in Table 5.2: Liquid Stream Treatment

Processes of the standard. Each area requir-

ing combustible gas detection monitoring is

listed in a clear, concise manner for ease of

understanding the application.

SOLUTIONS FOR PUMPING STATIONS AND WET WELLS The MSA TriGas Monitoring System (Figure

2) is an example of an integrated combus-

tible gas monitoring product that helps

plant operators comply with NFPA 820.

The system consists of up to three sen-

sors to alert personnel of gas leak hazards

with on-board alarming and communica-

tion interface to plant and remote location

control stations. Achieving NFPA 820 com-

pliance for pumping stations, lift stations,

influent headworks and wet wells associ-

ated with wastewater treatment plants that

are all subject to flooding is ideal for a gas

monitoring system with sample draw.

The system monitors for combustible

gases (for example, methane or petroleum

vapors), hydrogen sulfide and oxygen) and

offers sampling in high-moisture environ-

ments and poor access areas. Additional

features offer compliance with other

NFPA codes.

The system also is designed to accept sam-

ples from NEC Class I, Div. 2 areas from

wet wells with open channels that have

hazardous classification reduced by the

proper amount of air exchanges required.

OTHER FEATURES TO CONSIDERWhen selecting an integrated combustible

gas monitoring product, consider whether

the unit has additional mounting feet and

handles that allow it to be placed near a

confined-space entrance, alerting workers

as to the confined space’s atmospheric

conditions. This can be used to comply with

OSHA Standard 1910.148 Appendix E Sewer

System Entry guidelines when fixed gas

monitoring is required.

Dual-zone capability (Figure 3) provides

two independent systems housed in one

MONITORING SYSTEMFigure 2. The MSA TriGas Monitoring System uses as many as three sensors to alert personnel of gas leak hazards.



enclosure that monitors two sample points:

Pump module #1 is assigned to 0-100% LEL

CH4 and Pump module #2 is assigned to

0-50 pm H2S and 0-25% O2.

For dry wells and applications in which a

gas monitoring station is required with use

of remote sensors (Figure 4), mounting

the gas detector on a plate assembly with

power supply, horns and strobes can meet

site compliance with NFPA 820 standards.

In pumping station applications in which

end users do not need to house the gas

detection system components within a

wall-mounted enclosure and require only

DUAL-ZONE WET WELL MONITORING SYSTEMFigure 3. This type of system provides two sample points in a single enclosure.

DRY WELL GAS MONITORING SYSTEMFigure 4. When remote sensors are required, this type of setup can comply with NFPA 820 standards.



minimal features, a flow panel such can be

offered to meet basic NFPA 820 compli-

ance. This plate-mounted system includes

the necessary gas monitors, DC pump, flow

meter, three-way calibration valve and end-

line filter (Figure 5).

Other features to consider include heated

and/or NEMA 4X stainless steel enclosures;

capability with added protection to install

or handle samples in NEC Class I, Div. 1

areas where combustible gas is always

present; addition of alarm relay contacts

to meet needs of more complex alarming

logic; and additional water separator filters.

PROPER MONITORING FOR PROTECTIONMonitoring wastewater treatment plant

wells for combustible and toxic gases is

essential to protect employees, equipment

and the facilities themselves. Failing to

adhere to the requirements of NFPA Code

820 could result in an accident with tragic

or catastrophic consequences, including the

loss of life.

Multiple suppliers offer combustible and

toxic gas monitoring systems that meet

the requirements of NFPA Code 820. Their

field staffs are extremely knowledgeable

resources and welcome questions about

gas detection. The chances are excellent

that if you have a gas detection problem,

they’ve already heard it and solved it multi-

ple times at other treatment plants.

TIM WOLK is water and wastewater market sales

manager at MSA Safety. He can be reached at

[email protected].

WET WELL FLOW PANEL SYSTEMFigure 5. Flow panel systems such as the MSA TriGas Lite offers minimal features and can meet basic NFPA 820 compliance.



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