UNIVERSITY OF WEST HUNGARY

FACULTY OF AGRICULTURAL AND FOOD SCIENCES

WASTE WATER TREATMENT

IN THE UNITED KINGDOM

Balint Szule

PhD-student, NYME-MÉK, Mosonmagyaróvár

Correspondence:

Balint Szule

37 Creighton Road

London

N17 8JU

2014

2

Abstract:

The waste water treatment in the UK has a long history. It was obvious to collect

information from the UK, especially from London the capital city of the United

Kingdom (and one of the biggest city in the world). More than 10 million people live

and work in London. Collecting and treating this amount of waste water needs special

expertise and system. Having knowledge of other treatment methods from other

countries, is important to improve the system in Hungary. In this research the UK’s and

Hungarian’s waste water treatment were compared.

Key words: waste water, treatment, environmental, methods

Introduction

Freshwater is a vital natural resource that will continue to be renewable as long as it is

well managed. Preventing pollution from domestic, industrial, and agro-industrial

activities is important to ensure the sustainability of the locale’s development. (NG Wun

Jern, 2006)

In recent years in the UK all sewage water needs to be treated, whether it comes from a

home or a factory. The treatment are 99% takes place in the country and this work meet

the standard of the EU legislation.

Treatment of wastewater is an essential process that prevents contamination and the

destruction of our waterways, drinking water resources and natural water resources.

Although untreated waste water is mostly water (generally less than 0,1% is solid

material), without treatment the waste water produced every day would cause significant

damage to the environment. The removal of these solids and disinfection of the water

before discharge is the basic concept of wastewater treatment. If wastewater was

discharged without treatment directly to a receiving water system, it would severely

damage the water quality and render it unsuitable for swimming, fishing and other

activities. (URL1) The impacts of untreated waste water range from, chronic ecosystem

damage due to oxygen depletion of receiving waters from the biodegradation of organic

matter; ecosystem damage of eutrophication of waters resulting from excessive input of

nutrients present in waste water; potential health risks from water-born pathogens from

discharges to waters used for recreational activities. Wastewater is a carrier of harmful

bacteria and microorganisms known as pathogens. Several pathogens include

Cryptosporidium, Salmonella, Typhoid, E-Coli, Hepatitis A & B and Giardiasis also

3

known as “beaver fever”. Wastewater is also rich in nitrogen and phosphorus nutrients

which stimulate excessive aquatic growth, which in turn, can be detrimental to aquatic

life such as fish and waterfowl. Untreated waste water also contains sewage litter and

other sewage solids that can impact the environment, for example, through smothering

of river beds or posing a hazard through its ingestion by wildlife. (Waste water

treatment in the United Kingdom - 2012)

Discussion

Common regulation

In the United Kingdom the authority follows the European Union directive. The Council

Directive 91/271/EEC concerning urban waste-water treatment was adopted on 21 May

1991. Its objective is to protect the environment from the adverse effects of urban waste

water discharges and discharges from certain industrial sectors and concerns the

collection, treatment and discharge of:

Domestic waste water;

Mixture of waste water;

Waste water from certain industrial sectors;

Four main principles are laid down in the Directive:

1. Planning

2. Regulation

3. Monitoring

4. Information and reporting

Specifically the Directive requires:

The Collection and treatment of waste water in all agglomerations of> 2000

population equivalents;

Secondary treatment of all discharges from agglomerations of> 2000 p.e., and more

advanced treatment for agglomerations> 10 000 population equivalents in designated

sensitive areas and their catchments;

A requirement for pre-authorisation of all discharges of urban wastewater, of

discharges from the food-processing industry and of industrial discharges into urban

wastewater collection systems;

4

Monitoring of the performance of treatment plants and receiving waters; and

Controls of sewage sludge disposal and re-use, and treated waste water re-use

whenever it is appropriate.

1. Planning

The planning aspects of the Directive require Member States to:

Designate sensitive areas (sensitive water bodies) in accordance with three specific

criteria, and to review their designation every four years;

Identify the relevant hydraulic catchment areas of the sensitive areas and ensure that

all discharges from agglomerations with more than 10 000 p.e. located within the

catchment shall have more stringent than secondary treatment;

Establish less sensitive areas if relevant;

Establish a technical and financial programme for the implementation of the Directive

for the construction of sewage collecting systems and wastewater treatment plants

addressing treatment objectives within the deadlines set up by the Directive (and the

Accession Treaties for new Member States).

2. Regulation

The regulation aspects of the Directive require Member States to:

Establish systems of prior regulation or authorisation for all discharges of urban

wastewater;

Establish systems of prior regulation or authorisation for discharges of industrial

wastewater into urban sewage collecting systems to ensure:

o Treatment plant operation and sludge treatment will not be impeded;

o No adverse effect on the environment (including receiving waters) will occur;

and

o The safe disposal of sewage sludge.

Establish systems of prior regulation and/or specific authorisation and permits for food

processing industries;

Ensure that all urban wastewater generated in agglomerations with more than 2000

p.e. are supplied with collecting systems, and that the capacity of these is such that all

5

urban waste water is collected, taking account of normal local climatic conditions and

seasonal variations;

Ensure that national authorities take measures to limit pollution of receiving waters

from storm water overflows via collecting systems under unusual situations, such as

heavy rain;

Ensure that wastewater treatment is provided for all agglomerations at the level

specified by the Directive and within the required deadline:

o Secondary treatment is the basic level that should be provided, with more

stringent treatment being required in sensitive areas and their catchments;

o For certain discharges in coastal waters treatment may be less stringent (i.e.

primary treatment) under certain conditions and subject to the agreement of the

European Commission;

o For agglomerations with a population equivalent of less than 2000 but

equipped with a collecting system, appropriate treatment must be provided.

Ensure that technical requirements for the design, construction, operation and

maintenance of wastewater treatment plants treating urban wastewater are maintained

and that they ensure adequate capacity of the plant and treatment of urban wastewater

generated in agglomerations taking into account normal climatic conditions and

seasonal variations;

Ensure that the environment is protected from adverse effects of the discharge of

wastewater;

Ensure that the environmentally and technically sound reuse or disposal of sewage

sludge is subject to general rules, registration or authorisation and that the requirement

of specific inter-linked Directives for agricultural re-use (86/278/EEC), incineration

(89/429/EEC and 89/369/EEC), and landfill (99/31/EC) are respected. The disposal of

sewage sludge to surface waters is banned.

3. Monitoring

The monitoring aspects of the Directive require Member States to ensure that monitoring

programmes are in place and that the programmes correspond to the requirements laid down

in Annex I D of the Directive in terms of parameters monitored, analytical method and

6

sampling frequency. Member States are required to ensure that both discharges from urban

wastewater treatment plants and receiving waters are monitored.

4. Information and reporting

The information and reporting provisions of the Directive require Member States to ensure

that the following are put in place:

Adequate mechanisms to allow the co-operation and exchange of information with

other Member States in cases where discharges of wastewater have a transboundary

effect on water quality of shared waters;

Adequate reporting procedures and databases to allow the provision of information to

the Commission on:

o Transposition of the Directive into national legislation, implementation

programmes and situation reports on the disposal and re-use of treated urban

wastewater and sewage sludge;

o Status of collecting systems, efficiency of treatment plants (i.e. treatment level

and monitoring results) and the quality of receiving waters; and

o Status of discharges from the food-processing industry to surface waters;

Access for the public to relevant information and the publication of status reports

every two years on the status of wastewater collection and treatment and disposal or

re-use of sludge. (URL2)

The common law in the European Union speaks three different type of waste water. These are

the urban, domestic and industrial waste water. Urban waste water means domestic waste

water or the mixture of domestic waste water with industrial waste water and/or run-off

rainwater; domestic waste water means waste water from residential settlements and services

which originates predominantly from the human metabolism and from household activities.

Industrial waste water intend any waste water which is discharged from premises used for

carrying on any trade or industry, other than domestic waste water and run-off rainwater

(Urban waste water directive /91/271/ECC).

Sewage treatment is the process of removing contaminants from wastewater, including

household sewage and run off (effluents). It includes physical, chemical, and biological

processes to remove physical, chemical and biological contaminants. Its objective is to

produce an environmentally safe fluid waste stream (or treated effluent) and a solid waste (or

7

treated sludge) suitable for disposal or reuse (usually as farm fertilizer). With suitable

technology, it is possible to re-use sewage effluent for drinking water, although this is usually

only done in places with limited water supplies. (URL3)

Most wastewater treatment processes have three main disadvantage (URL4):

high energy requirements;

high operation and maintenance requirements, including production of large

volumes of sludge (solid waste material);

they are geared towards environmental prohibition rather than human health

protection.

History of wastewater treatment

Many ancient cities had drainage systems, but they were primarily intended to carry rainwater

away from roofs and pavements. A notable example is the drainage system of ancient Rome.

It included many surface conduits that were connected to a large vaulted channel called the

Cloaca Maxima (“Great Sewer”), which carried drainage water to the Tiber River. Built of

stone and on a grand scale, the Cloaca Maxima is one of the oldest existing monuments of

Roman engineering.

There was little progress in urban drainage or sewerage during the Middle Ages. Privy vaults

and cesspools were used, but most wastes were simply dumped into gutters to be flushed

through the drains by floods. Toilets (water closets) were installed in houses in the early 19th

century, but they were usually connected to cesspools, not to sewers. In densely populated

areas, local conditions soon became intolerable because the cesspools were seldom emptied

and frequently overflowed. The threat to public health became apparent. In England in the

middle of the 19th century, outbreaks of cholera were traced directly to well-water supplies

contaminated with human waste from privy vaults and cesspools. It soon became necessary

for all water closets in the larger towns to be connected directly to the storm sewers. This

transferred sewage from the ground near houses to nearby bodies of water. Thus, a new

problem emerged: surface water pollution.

It used to be said that “the solution to pollution is dilution.” When small amounts of sewage

are discharged into a flowing body of water, a natural process of stream self-purification

occurs. Densely populated communities generate such large quantities of sewage, however,

that dilution alone does not prevent pollution. This makes it necessary to treat or purify

8

wastewater to some degree before disposal. As populations in towns and cities grew the rivers

could not absorb the pollution. They began to smell and became unable to support life. The

situation was particularly serious in London and culminated in the House of Commons having

to suspended as a result of the “Great Stink” from the Thames in 1859. This encouraged the

construction of a new sewer system in London that set the standard for the rest of the country.

The construction of centralized sewage treatment plants began in the late 19th

and early 20th

centuries, principally in the United Kingdom and the United States. Instead of discharging

sewage directly into a nearby body of water, it was first passed through a combination of

physical, biological, and chemical processes that removed some or most of the pollutants.

Also beginning in the 1900s, new sewage-collection systems were designed to separate storm

water from domestic wastewater, so that treatment plants did not become overloaded during

periods of wet weather.

After the middle of the 20th century, increasing public concern for environmental quality led

to broader and more stringent regulation of wastewater disposal practices. Higher levels of

treatment were required. For example, pretreatment of industrial wastewater, with the aim of

preventing toxic chemicals from interfering with the biological processes used at sewage

treatment plants, often became a necessity. In fact, wastewater treatment technology advanced

to the point where it became possible to remove virtually all pollutants from sewage. This was

so expensive, however, that such high levels of treatment were not usually justified.

Wastewater treatment plants became large, complex facilities that required considerable

amounts of energy for their operation. After the rise of oil prices in the 1970s, concern for

energy conservation became a more important factor in the design of new pollution control

systems. Consequently, land disposal and subsurface disposal of sewage began to receive

increased attention where feasible. Such “low-tech” pollution control methods not only might

help to conserve energy but also might serve to recycle nutrients and replenish groundwater

supplies. (URL5)

Treatment

Collection

Before waste water can be treated it needs to be collected. Every day in the UK over 624,200

kilometres of sewers collect over 11 billion litres of waste water from homes, municipal,

commercial and industrial premises and rainwater run-off from roads and other impermeable

surfaces.

9

This is treated at about 9,000 sewage treatment works before the treated effluent is discharged

to inland waters, estuaries and the sea. (URL6)

The UK’s sewerage undertakers are responsible for building, maintaining and improving main

sewers, pumping stations, and waste water treatment facilities that service around 96% of the

UK population. The remaining 4% of the population, represented by the smallest of

communities and individual properties in rural areas remote from mains sewers, are generally

served by privately owned, small-package treatment plants catering for small groups of

houses, to septic tanks, cesspits and other in-situ treatment systems, generally serving

individual properties. There are three main types of collection system:

surface-water drainage that collects rainwater run-off from roads and urban areas and

discharge direct to local waters;

combined sewerage that collects rainwater run-off and waste water from domestic,

industrial, commercial and other premises; and

foul drainage that collects domestic waste water from premises (no rainwater is

collected).

Both surface water and foul drainage may eventually connect to combined sewerage where

there are no local environmental waters to which surface water drainage can discharge.

Combined sewerage systems are not uncommon in the UK and elsewhere in Europe. A basic

requirement of combined sewerage systems is that they need to cater for all normal local

climatic conditions. In other words, they need to be large enough to receive and effectively

manage storm water from peak seasonal wet weather. However, even when designed to deal

with such weather, there may be times when heavy continuous rainfall will temporarily

exceed the capacity of combined sewerage systems. To deal with such situations ‘combined

sewer overflows’ are designed and built as an integral part of combined sewerage systems.

The purpose of combined sewer overflows is to allow excess waste water to be discharged to

local waters to avoid sewers being overwhelmed and waste water ‘backing up’ along sewers

and flooding streets and properties, or overwhelming waste water treatment plants. The

backflow of waste water to properties and streets would present human health hazards and

flooded and overflowing treatment plants would disrupt treatment processes and have the

potential to cause more environmental damage than can be caused by discharges from

combined sewer overflows. (Waste Water Treatment in the UK, 2012)

10

Treatment methods

Usually wastewater treatment will involve collecting the wastewater in a central, segregated

location (the Wastewater Treatment Plant) and subjecting the wastewater to various treatment

processes. Most often, since large volumes of wastewater are involved, treatment processes

are carried out on continuously flowing wastewaters (continuous flow or "open" systems)

rather than as "batch" or a series of periodic treatment processes in which treatment is carried

out on parcels or "batches" of wastewaters. While most wastewater treatment processes are

continuous flow, certain operations, such as vacuum filtration, involving as it does, storage of

sludge, the addition of chemicals, filtration and removal or disposal of the treated sludge, are

routinely handled as periodic batch operations. Wastewater treatment, however, can also be

organized or categorized by the nature of the treatment process operation being used; for

example, physical, chemical or biological. Examples of these treatment steps are shown

below. A complete treatment system may consist of the application of a number of physical,

chemical and biological processes to the wastewater.

Physical Chemical Biological

Sedimentation

(Clarification)

Chlorination Aerobic

Screening Ozonation Activated Sludge Treatment

Methods

Aeration Neutralization Trickling Filtration

Filtration Coagulation Oxidation Ponds

Flotation and Skimming Adsorption Lagoons

Degassification Ion Exchange Aerobic Digestion

Equalization Anaerobic

Lagoons

Septic Tanks

Table 1: Some Physical, Chemical and Biological Wastewater Treatment Methods (Source: URL7)

Conventional wastewater treatment consists of a combination of physical, chemical, and

biological processes and operations to remove solids, organic matter and, sometimes,

nutrients from wastewater. General terms used to describe different degrees of treatment, in

order of increasing treatment level, are preliminary, primary, secondary, and tertiary and/or

advanced wastewater treatment.

11

Figure 3: Generalized flow diagram for

municipal wastewater treatment (Asano et

al. 1985)

Preliminary treatment

The objective of preliminary treatment is the removal of coarse solids and other large

materials often found in raw wastewater. Removal of these materials is necessary to enhance

the operation and maintenance of subsequent treatment units. Preliminary treatment

operations typically include coarse screening, grit removal and, in some cases, comminution

of large objects.

Figure 4: Simplified process flow diagram

for a typical large-scale treatment plant

(Source: URL8)

Screens

On entering a sewage treatment works,

dirty water passes through screens to

remove paper, wood and other large

articles that could damage machinery

or block pipe systems. Screens consist of vertical bars spaced close together or perforated

plates that are cleaned by rakes or water jets. The cleared material (known as screenings) is

washed and safely disposed of at a landfill site. It is important to cut the amount of screenings

which can block sewers before the treatment works with unpleasant results. Only toilet paper

should be flushed down the toilet. Water companies run ‘Bag It and Bin It’ campaign to

encourage the public not to flush cotton buds or plastic and sanitary items. In some European

countries the sewer pipes are so small that not even paper may be flushed.

12

Grit Removal

Grit includes sand, gravel, cinder, or other heavy solid materials that are “heavier” (higher

specific gravity) than the organic biodegradable solids in the wastewater. Grit also includes

eggshells, bone chips, seeds, coffee grounds, and large organic particles, such as food waste.

Removal of grit prevents unnecessary abrasion and wear of mechanical equipment, grit

deposition in pipelines and channels, and accumulation of grit in anaerobic digesters and

aeration basins. Grit removal facilities typically precede primary clarification, and follow

screening and comminution. This prevents large solids from interfering with grit handling

equipment. In secondary treatment plants without primary clarification, grit removal should

precede aeration (Metcalf and Eddy, 1991)

In grit chambers, the velocity of the water through the chamber is maintained sufficiently

high, or air is used, so as to prevent the settling of most organic solids. Grit removal is not

included as a preliminary treatment step in most small wastewater treatment plants.

Comminutors are sometimes adopted to supplement coarse screening and serve to reduce the

size of large particles so that they will be removed in the form of a sludge in subsequent

treatment processes. Flow measurement devices, often standing-wave flumes, are always

included at the preliminary treatment stage.

Removal of oil and grease

At some treatment works this process is thought necessary to protect the downstream

processes. Materials such as oil and grease should not be poured down drains or discharged to

a sewer

Primary treatment

The objective of primary treatment is the removal of settleable organic and inorganic solids

by sedimentation, and the removal of materials that will float (scum) by skimming.

Approximately 25 to 50% of the incoming biochemical oxygen demand (BOD5), 50 to 70% of

the total suspended solids (SS), and 65% of the oil and grease are removed during primary

treatment. Some organic nitrogen, organic phosphorus, and heavy metals associated with

solids are also removed during primary sedimentation but colloidal and dissolved constituents

are not affected. The effluent from primary sedimentation units is referred to as primary

effluent.

13

In many industrialized countries, primary treatment is the minimum level of preapplication

treatment required for wastewater irrigation. It may be considered sufficient treatment if the

wastewater is used to irrigate crops that are not consumed by humans or to irrigate orchards,

vineyards, and some processed food crops. However, to prevent potential nuisance conditions

in storage or flow-equalizing reservoirs, some form of secondary treatment is normally

required in these countries, even in the case of non-food crop irrigation. It may be possible to

use at least a portion of primary effluent for irrigation if off-line storage is provided.

Primary sedimentation tanks or clarifiers may be round or rectangular basins, typically 3 to 5

m deep, with hydraulic retention time between 2 and 3 hours. Settled solids (primary sludge)

are normally removed from the bottom of tanks by sludge rakes that scrape the sludge to a

central well from which it is pumped to sludge processing units. Scum is swept across the

tank surface by water jets or mechanical means from which it is also pumped to sludge

processing units.

In large sewage treatment plants, primary sludge is most commonly processed biologically by

anaerobic digestion. In the digestion process, anaerobic and facultative bacteria metabolize

the organic material in sludge, thereby reducing the volume requiring ultimate disposal,

making the sludge stable (nonputrescible) and improving its dewatering characteristics.

Digestion is carried out in covered tanks (anaerobic digesters), typically 7 to 14 m deep. The

residence time in a digester may vary from a minimum of about 10 days for high-rate

digesters (well-mixed and heated) to 60 days or more in standard-rate digesters. Gas

containing about 60 to 65% methane is produced during digestion and can be recovered as an

energy source. In small sewage treatment plants, sludge is processed in a variety of ways

including: aerobic digestion, storage in sludge lagoons, direct application to sludge drying

beds, in-process storage (as in stabilization ponds), and land application.

Secondary treatment

The settlement process is very effective in removing organic material, but if the settled

sewage were discharged to a watercourse, the dissolved organic matter in settled sewage

would still cause problems. The objective of secondary treatment is the further treatment of

the effluent from primary treatment to remove the residual organics and suspended solids. In

most cases, secondary treatment follows primary treatment and involves the removal of

biodegradable dissolved and colloidal organic matter using aerobic biological treatment

processes. Aerobic biological treatment is performed in the presence of oxygen by aerobic

microorganisms (principally bacteria) that metabolize the organic matter in the wastewater,

14

thereby producing more microorganisms and inorganic end-products (principally CO2, NH3,

and H2O). Several aerobic biological processes are used for secondary treatment differing

primarily in the manner in which oxygen is supplied to the microorganisms and in the rate at

which organisms metabolize the organic matter.

High-rate biological processes are characterized by relatively small reactor volumes and high

concentrations of microorganisms compared with low rate processes. Consequently, the

growth rate of new organisms is much greater in high-rate systems because of the well

controlled environment. The microorganisms must be separated from the treated wastewater

by sedimentation to produce clarified secondary effluent. The sedimentation tanks used in

secondary treatment, often referred to as secondary clarifiers, operate in the same basic

manner as the primary clarifiers described previously. The biological solids removed during

secondary sedimentation, called secondary or biological sludge, are normally combined with

primary sludge for sludge processing.

Common high-rate processes include the activated sludge processes, trickling filters or

biofilters, oxidation ditches, and rotating biological contactors (RBC). A combination of two

of these processes in series (e.g., biofilter followed by activated sludge) is sometimes used to

treat municipal wastewater containing a high concentration of organic material from industrial

sources.

Activated Sludge

In the activated sludge process, the dispersed-growth reactor is an aeration tank or basin

containing a suspension of the wastewater and microorganisms, the mixed liquor. The

contents of the aeration tank are mixed vigorously by aeration devices which also supply

oxygen to the biological suspension. Aeration devices commonly used include submerged

diffusers that release compressed air and mechanical surface aerators that introduce air by

agitating the liquid surface. Hydraulic retention time in the aeration tanks usually ranges from

3 to 8 hours but can be higher with high BOD5 wastewaters. Following the aeration step, the

microorganisms are separated from the liquid by sedimentation and the clarified liquid is

secondary effluent. A portion of the biological sludge is recycled to the aeration basin to

maintain a high mixed-liquor suspended solids (MLSS) level. The remainder is removed from

the process and sent to sludge processing to maintain a relatively constant concentration of

microorganisms in the system. Several variations of the basic activated sludge process, such

as extended aeration and oxidation ditches, are in common use, but the principles are similar.

15

An adaptation of the activated sludge process is often used to remove nitrogen and

phosphorus. Effluent from primary clarifiers flows to the biological reactor, which is

physically divided into five zones by baffles and weirs. In sequence these zones are:

anaerobic fermentation zone (characterized by very low dissolved oxygen levels and

the absence of nitrates);

anoxic zone (low dissolved oxygen levels but nitrates present);

aerobic zone (aerated);

secondary anoxic zone; and

final aeration zone.

The function of the first zone is to condition the group of bacteria responsible for phosphorus

removal by stressing them under low oxidation-reduction conditions, which results in a

release of phosphorus equilibrium in the cells of the bacteria. On subsequent exposure to an

adequate supply of oxygen and phosphorus in the aerated zones, these cells rapidly

accumulate phosphorus considerably in excess of their normal metabolic requirements.

Phosphorus is removed from the system with the waste activated sludge.

Most of the nitrogen in the influent is in the ammonia form, and this passes through the first

two zones virtually unaltered. In the third aerobic zone, the sludge age is such that almost

complete nitrification takes place, and the ammonia nitrogen is converted to nitrites and then

to nitrates. The nitrate-rich mixed liquor is then recycled from the aerobic zone back to the

first anoxic zone. Here denitrification occurs, where the recycled nitrates, in the absence of

dissolved oxygen, are reduced by facultative bacteria to nitrogen gas, using the influent

organic carbon compounds as hydrogen donors. The nitrogen gas merely escapes to

atmosphere. In the second anoxic zone, those nitrates which were not recycled are reduced by

the endogenous respiration of bacteria. In the final re-aeration zone, dissolved oxygen levels

are again raised to prevent further denitrification, which would impair settling in the

secondary clarifiers to which the mixed liquor then flows.

An experimentation programme on this plant demonstrated the importance of the addition of

volatile fatty acids to the anaerobic fermentation zone to achieve good phosphorus removal.

These essential short-chain organics (mainly acetates) are produced by the controlled

fermentation of primary sludge in a gravity thickener and are released into the thickener

supernatent, which can be fed to the head of the biological reactor. Without this supernatent

return flow, overall phosphorus removal quickly dropped to levels found in conventional

activated sludge plants.

16

In many situations, where the risk of public exposure to the reclaimed water or residual

constituents is high, the intent of the treatment is to minimize the probability of human

exposure to enteric viruses and other pathogens. Effective disinfection of viruses is believed

to be inhibited by suspended and colloidal solids in the water, therefore these solids must be

removed by advanced treatment before the disinfection step.

Trickling Filters

A trickling filter or biofilter consists of a basin or tower filled with support media such as

stones, plastic shapes, or wooden slats. Wastewater is applied intermittently, or sometimes

continuously, over the media. Microorganisms become attached to the media and form a

biological layer or fixed film. Organic matter in the wastewater diffuses into the film, where it

is metabolized. Oxygen is normally supplied to the film by the natural flow of air either up or

down through the media, depending on the relative temperatures of the wastewater and

ambient air. Forced air can also be supplied by blowers but this is rarely necessary. The

thickness of the biofilm increases as new organisms grow. Periodically, portions of the film

'slough off the media. The sloughed material is separated from the liquid in a secondary

clarifier and discharged to sludge processing. Clarified liquid from the secondary clarifier is

the secondary effluent and a portion is often recycled to the biofilter to improve hydraulic

distribution of the wastewater over the filter.

Rotating Biological Contactors

Rotating biological contactors (RBCs) are fixed-film reactors similar to biofilters in that

organisms are attached to support media. In the case of the RBC, the support media are slowly

rotating discs that are partially submerged in flowing wastewater in the reactor. Oxygen is

supplied to the attached biofilm from the air when the film is out of the water and from the

liquid when submerged, since oxygen is transferred to the wastewater by surface turbulence

created by the discs' rotation. Sloughed pieces of biofilm are removed in the same manner

described for biofilters.

High-rate biological treatment processes, in combination with primary sedimentation,

typically remove 85 % of the BOD5 and SS originally present in the raw wastewater and some

of the heavy metals. Activated sludge generally produces an effluent of slightly higher

quality, in terms of these constituents, than biofilters or RBCs. When coupled with a

disinfection step, these processes can provide substantial but not complete removal of bacteria

17

and virus. However, they remove very little phosphorus, nitrogen, non-biodegradable

organics, or dissolved minerals.

Tertiary and/or advanced treatment

Tertiary and/or advanced wastewater treatment is employed when specific wastewater

constituents which cannot be removed by secondary treatment must be removed. As shown in

Figure 3, individual treatment processes are necessary to remove nitrogen, phosphorus,

additional suspended solids, refractory organics, heavy metals and dissolved solids. Because

advanced treatment usually follows high-rate secondary treatment, it is sometimes referred to

as tertiary treatment. However, advanced treatment processes are sometimes combined with

primary or secondary treatment (e.g., chemical addition to primary clarifiers or aeration basins

to remove phosphorus) or used in place of secondary treatment (e.g., overland flow treatment

of primary effluent).

Disinfection

Disinfection normally involves the injection of a chlorine solution at the head end of a

chlorine contact basin. The chlorine dosage depends upon the strength of the wastewater and

other factors, but dosages of 5 to 15 mg/l are common.

Ozone and ultraviolet (uv) irradiation can also be used for disinfection but these methods of

disinfection are not in common use.

Figure 5: Ultraviolet (UV)

irradiation at South-Pest Wastewater

Treatment Plan, Hungary

Chlorine contact basins are

usually rectangular channels,

with baffles to prevent short-

circuiting, designed to provide a

contact time of about 30

minutes. However, to meet

advanced wastewater treatment

requirements, a chlorine contact time of as long as 120 minutes is sometimes required for

specific irrigation uses of reclaimed wastewater. The bactericidal effects of chlorine and other

disinfectants are dependent upon pH, contact time, organic content, and effluent temperature.

18

Conclusion

The world’s water is limited and valuable. It is continually used and reused in the water cycle.

Every day in the UK about 624,200 kilometres of sewers collect over 11 billion litres of waste

water. This is treated at about 9,000 sewage treatment works before the treated effluent is

discharged to inland waters, estuaries and the sea.

Waste water is the mixture of domestic waste water from the kitchens, bathrooms and toilets,

the waste water from industries discharging to sewers and rainwater run-off from roads and

other impermeable surfaces such as roofs, pavements, and roads draining to sewers.

Without treatment the water from toilets, baths, sinks and washing machines from domestic

and residential premises, industrial waste water discharges to sewers and the rainwater

contaminated with metals, oils and other pollutants in rainwater run-off from urban areas

draining to sewers would have significant adverse impacts on the water environment.

Without suitable treatment, the waste water we produce every day would damage the water

environment and create public health problems. Untreated sewage contains organic matter,

bacteria and chemicals. The impacts of untreated waste water range from, chronic ecosystem

damage due to oxygen depletion of receiving waters from the biodegradation of organic

matter; ecosystem damage of eutrophication of waters resulting from excessive inputs of

nutrients present in waste water; potential health risks from water-borne pathogens from

discharges to waters used for recreational activities, such as swimming and canoeing.

Untreated waste water also contains sewage litter and other sewage solids that can impact the

environment, for example, trough the smothering of river beds or posing a hazard through its

ingestion by wildlife.

In a modern society wastewater is carried from houses in underground pipes or sewers. In

older parts of towns and cities sewers may also collect rainwater from roofs and roadways.

Sewage received at the treatment works is normally greyish in colour with a slight ‘fruity’

smell and an occasional tint of ‘bad eggs’. It is basically dirty water less than 0,1% being

waste that needs to be treated.

There are four main stages in wastewater treatment; preliminary, primary, secondary

(biological) and tertiary treatment. The number of stages applied depends on the quality of

discharge required to protect the environment.

I

References

1. Alabaster, J.S. - Lloyd R. (1980): Water Quality Criteria for Freshwater Fish.

Butterworths, London.

2. Allan, J. A. (2003): Integrated water resources management is more a political than a

technical challenge, Developments in Water Science, Vol. 50, 9-23. p.

3. Arar A. (1988): Background to treatment and use of sewage effluent. Ch. 2, Treatment

and Use of Sewage Effluent for Irrigation, M.B. Pescod and A. Arar (eds).

Butterworths, Sevenoaks, Kent.

4. Asano, T. - Smit, R. G. - Tchobanoglous, G. (1985): Municipal wastewater: Treatment

and reclaimed water characteristics. In: Irrigation with reclaimed municipal

wastewater - a guidance manual, Lewise Publishers, Chelsea, United Kingdom.

5. Barth, E. F. (1971): Perspectives on Wastewater Treatment Processes: Physical-

Chemical and Biological Journal, Water Environment Federation, Vol. 43, No. 11.,

2189-2194. p.

6. Cooper, P.F. (1999): A review of the design and performance of vertical flow and

hybrid reed bed treatment systems. Water Sciences and Technology, Vol. 40, no. 3, 1-

9. p.

7. Henze, M. - Harremoës, P. - Arvin, E. - Jes la Cour Jansen. (2002): Wastewater

Treatment: Biological and Chemical Processes, Springer – Verlag, Berlin, Germany.

8. Hillman, P.J. (1988): Health aspects of reuse of treated wastewater for irrigation. Ch.

5, Treatment and Use of Sewage Effluent for Irrigation. M.B. Pescod and A. Arar

(eds). Butterworths, Sevenoaks, Kent.

9. Hussain I.- Raschid, L. - Hanjra, M. A. - Marikar, F. - W. van der Hoek, (2002):

Wastewater use in agriculture: Review of impacts and methodological issues in

valuing impacts, International Water Management Institute, Colombo, Sri Lanka.

10. Infrastructure Delivery Plan, (2011): Royal Borough of Kingston upon Thames, Local

Development Framework.

11. Marco, A. - Esplugas, S. - Saum, G. (1997): How and why combine chemical and

biological processes for wastewater treatment, Water Science and Technology, Vol.

35, Issue 4, 321–327. p.

12. Metcalf and Eddy (1991): Narragansett Bay combined sewage overflows,

Environmental Protection Agency, Region I: Rhode Island, Department of

Environmental Management, United States.

II

13. NG Wun Jern (2006): Industrial Wastewater Treatment, Imperial College Press,

London.

14. Parr, J. - Smith, M.- Shaw, R. (2010): Wastewater Treatment Option, Water and

Environmental Health at London and Loughborough, Loughborough University,

Leicestershire, United Kingdom.

15. Punt, A. - Wood, MD. - Rose, D. (2007): Radionuclide discharges to sewer: A field

investigation. Environment Agency, Bristol. pp 53.

16. Sidle, R. C. - Hook, J. E. - Kardos L. T. (1976): Heavy metal application and plant

uptake in a land disposal system for wastewater. Journal of Environmental Quality.

Vol. 5, no. 1, 97-102. p.

17. Somlyody, L. – Shanahan, P. (1998): Municipal wastewater treatment in Central and

Eastern Europe: Present situation and cost-effective development strategies.

Washington, D.C.: World Bank. Pp. xvi, 145.

18. Stephenson, T. - Judd, S. - Jefferson, B. - Brindle, K. (2000): Membrane Bioreactors

for Wastewater Treatment, IWA Publishing, London, United Kingdom.

19. Syme, G. J. - Nancarrow, B. E. (1997): The determinants of perception of fairness in

the allocation of water to multiple uses. Water Resources Research. Vol. 33, no. 9,

2143-2152. p.

20. Takashi and Audrey D. Levine. (1996): Wastewater reclamation, recycling and reuse:

past, present, and future, Water Science and Technology, Vol. 33, no. 10-11, 1-14. p.

21. Waste water treatment in the United Kingdom - 2012 - Implementation of the

European Union Urban, Waste Water Treatment Directive-91/271/EEC, DEFRA,

London, 2012.

22. World Bank (2012): A primer on energy efficiency for municipal water and

wastewater utilities. Energy Sector Management Assistance Program, Technical

Report, Washington, DC, World Bank

23. URL1:http://www.barrie.ca/LIVING/ENVIRONMENT/WASTEWATERTREATME

NT/Pages/default.aspx

24. URL2: http://www.irsociety.co.uk/Archives/8/north_surrey_joint.htm

25. URL3:http://edithsstreets.blogspot.co.uk/2010/12/thames-tributary-hogsmill-

norbiton.html

26. URL4:http://ec.europa.eu/environment/water/water-

urbanwaste/directiveprinciples/index_en.htm#planning

III

27. URL5:http://www.lboro.ac.uk/well/resources/technical-briefs/64-wastewater-

treatment-options.pdf

28. URL6:http://www.britannica.com/EBchecked/topic/666611/wastewater-treatment

29. URL7:www.gov.uk