Transcript
DESIGN OBJECTIVES
Your goal is to find the best solution to meet the Client’s 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 environment
OBJECTIVES 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 cost
How well each alternative satisfies a criteria is frequently a subjective judgement, since it doesn’t
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 don’t 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 plants
Factor
explanation
climate (constraint?)
temp affects rxn rates, freezing conditions can affect
phys operation
meet permit (constraint)
BOD, TSS, DO, coliform, pH,
exceed – criteria
ammonia, NO3, NO2, P,...
public acceptance
aesthetic appearance, odor, traffic, etc.
odor
potential to generate odor; uncontrolled releases
past experience
applied at other WWTPs
requires pilot testing
not enough information available to design and
estimate performance without pilot tests
environmental impact
surface water, groundwater, biosolids, ecosystems
plant personnel capable of
already trained; more training needed, more personnel
operating
needed
energy conservation
due to energy costs; to conserve
capital cost
initial costs to construct the process on site
O&M cost
yearly operation and maintenance costs
complexity
how difficult to operate under routine conditions and
under shock loads; difficulty fixing when broken;
ease of construction
flexibility
process can accommodate longterm change in influent
quantity, quality, or regulatory requirement by
adjusting operating parameters
reliability
tendency for minimal mechanical equipment failure
resulting in down time;
stability
stability of process under short-term stressed
conditions; ease of correcting upsets
chemical requirements
either desire or do not desire to use chemicals in the
treatment processes
safety
to operators, public
residuals
handling, cost, beneficial use
modularity
easy 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 facilities
does not abandon existing facilities but utilizes them to
the optimal extent
negative impacts to existing
will not require changes in existing upstream or
processes
downstream processes
serving water treatment
handling chemical sludges from drinking water
plant & industries
treatment; industrial wastewater flows/quality
weight