DESIGN OBJECTIVES

DESIGN OBJECTIVES

Your goal is to find the best solution to meet the Clients wastewater treatment needs over the next 20 years. How do you design a solution that optimally achieves the goals & objectives of the project?

1. First, you must first define the goals & objectives.GOALS should reflect the ultimate purposes of those who have both direct and indirect interests in the project.

example: to produce safe effluent water that protects human health and the environmentOBJECTIVES specify which characteristics of the system are to be optimized in order to achieve the goals. Things such as cost, aesthetics, etc.

ecample: maximize the safety of the plant

2. Then specify the criteria against which you will measure how well the goals/objectives are met

CONSTRAINTS: drive the alternatives selection and design by mandating limits that cannot be exceeded

these MAY be legal limits

examples: must fit the WWRF on the available land

must comply with NPDES permit limits from the state

must comply with water rights

maximum amount of money (potentially)

CRITERIA: are desirable or undesirable elements against which the design will be judged; a set of parameters used to measure how optimum a solution is with respect to the objectives

Criteria are subject to interpretation !

As the design team you need to balance your professional judgement with both the Client concerns and public concerns.Non-technical issues have a large impact on the final design

social, economic, & political issues should be considered

Frequently, the goals, objectives, and criteria may conflict; therefore, it is important to rank the relative importance of each. Example: optimal water quality vs low costHow well each alternative satisfies a criteria is frequently a subjective judgement, since it doesnt involve quantifiable elements

Due to the complexity of our problem, and the HUGE range of possible combinations of processes to achieve our goals, your team will likely need to discretize the problems.Example A

1. primary treatment of all WW flow

2. secondary treatment of all WW flow

3. advanced treatment of all WW flow

for next 5 years, remove ammonia

in 10 to 15 yrs, need to remove N

in 15 to 20 yrs, need to remove P

Example B

1. meet Q and effluent limits for next 5 years

2. meet Q and effluent limits for 5-15 yrs

3. meet Q and effluent limits for 15-20 yrs

Example C

1. remove solids

2. remove BOD

3. remove bacteria

4. remove ammonia

5. remove N & P (for reuse, or in 15-20 yrs)

6. treat biosolids

Example D: unit processes

1. primary settlers

2. activated sludge

3. biotrickling filters

etc.....

** first cut: eliminate things that dont meet CONSTRAINTS

** next: primary criteria? main criteria with sub-criteria?

-> try to narrow to 3 to 5 options for detailed evaluation (1/person)

** listing the criteria is not enough -- need to include a sentence or 2 definition, so that everyone will interpret each criteria the same

COMMUNICATION IS VITAL TO DEFINE AND WEIGHT DESIGN OBJECTIVES

1. NORMAL

1. EXTERNAL - design engineers with clients, stakeholders

* meetings & presentations

* town meetings with presentations & Q/A

* workshops (1-2 days)

- written via surveys, letters, e-mail

2. INTERNAL - within design firm or team

* brainstorming

* informal presentations

* exchange written proposal, sketches, calcs

* circulate among whole team

2. CONFLICT RESOLUTION

1. EXTERNAL

- due to miscommunication

(most conflict can be avoided by good, open communication)

- client or engineer making criteria into constraints

(not enough flexibility)

- ethical

- may require a 3rd party mediator to resolve

DECISION MATRIX AN EFFECTIVE TOOL TO COMPARE & PRESENT RESULTS

CAN RUN A COST:BENEFIT ANALYSIS FOR EACH ALTERNATIVE; PICK ALTERNATIVE WITH HIGHEST B/C RATIO

Examples of constraints and criteria applicable for wastewater treatment plantsFactorexplanationweight

climate (constraint?)temp affects rxn rates, freezing conditions can affect phys operation

meet permit (constraint)

exceed criteriaBOD, TSS, DO, coliform, pH,

ammonia, NO3, NO2, P,...

public acceptanceaesthetic appearance, odor, traffic, etc.

odorpotential to generate odor; uncontrolled releases

past experienceapplied at other WWTPs

requires pilot testingnot enough information available to design and estimate performance without pilot tests

environmental impactsurface water, groundwater, biosolids, ecosystems

plant personnel capable of operatingalready trained; more training needed, more personnel needed

energy conservationdue to energy costs; to conserve

capital costinitial costs to construct the process on site

O&M costyearly operation and maintenance costs

complexityhow difficult to operate under routine conditions and under shock loads; difficulty fixing when broken;

ease of construction

flexibilityprocess can accommodate longterm change in influent quantity, quality, or regulatory requirement by adjusting operating parameters

reliabilitytendency for minimal mechanical equipment failure resulting in down time;

stabilitystability of process under short-term stressed conditions; ease of correcting upsets

chemical requirementseither desire or do not desire to use chemicals in the treatment processes

safetyto operators, public

residualshandling, cost, beneficial use

modularityeasy to upgrade with similar processes due to modular design; take one portion out of service for repair while maintaining operation of others

use of existing facilitiesdoes not abandon existing facilities but utilizes them to the optimal extent

negative impacts to existing processeswill not require changes in existing upstream or downstream processes

serving water treatment plant & industrieshandling chemical sludges from drinking water treatment; industrial wastewater flows/quality