Download - Waste disposal and decomposition
Waste disposal and
decomposition
Landfills: problems with cost, availability, ground-water pollution, liquid content, methane production.
Oceans: the “Victoria” solution, Seattle’s Lake Washington and
Puget Sound experience.
Incineration; problems with location, NIMBY, Not In My BackYard
Options for sewage disposal
In the 1950’s demonstration by Professor Tommy Edmondson that the Lake Washington ecosystem had been substantially changed due to discharge of effluent. Nitrogen pollution
In 1958 voters in Seattle and King County created Metro, an agency charged with creating a regional wastewater treatment system.
In 1966 construction of a primary treatment plant completed at West Point with discharge into Puget Sound.
1972 Federal Clean Water Act
In 1972 first biosolids applications at Pack Forest
In 1991 Metro begins an expansion of the plant West Point plant
Some developments leading to recycling
Quantities and collection
Biology and engineering of treatment
Recycling through biosolids application
RecyclingThe principle is: (1) to use a treatment plant to remove soluble nitrogen from the effluent and kill pathogens, and (2) to apply the solid processed from bacterial matter to agricultural fields, forests, and land requiring re-medial treatment
There are problems associated with:
Total Suspended Solids loading (average annual) 181,000 lbs/day
Electricity generated 7,437,972 kilowatt hours
Biosolids produced 53,409 wet tons; 13,277 dry tons per year
Reclaimed water used 0.61 mgd
Outfall 3,600 ft. offshore; 240 ft. deep; 500 ft. diffuser
Annual budget for King County: Operating, $82 million; Capital, $96 million
At the West Point plant:
In King County 95% of the wastewater is from homes and businesses, with only 5% from industries
Quantities and Collection
Two waste water treatment plants in King County
Average daily capacity of the West plant is 133 million gallons per day
Biology and engineering of treatment
Most organic matter is converted by micro–organisms to inorganic forms. This process is called mineralization.
Large molecules will first be broken down to smaller ones by bacterial exo-enzymes, enzymes that bacteria excrete.
The most important organisms involved in these conversions are heterotrophic bacteria.
It is extremely difficult to identify bacterial genera, let alone species, from water purification systems, but it is obvious that the genera Flavobacterium and Pseudomonas are important.
Overview of treatment
O2 + bacteria + dissolved and suspended organic matter
Screen
Gritchamber
Secondary treatment
Primary treatment Skim
and settle solids
Solids processing
Blend
ThickenHeat
Methane
Anaerobic bacterial digestion
Centrifuge
Chlorination
Puget Sound
Settled biomass
High Purity Oxygen activated sludge process
West Point Treatment Plant
Nitrogen removal into biomass
Nitrogen metabo;ism
mean cellresidence times
Nitrogen is incorporated into microbial biomass. Two types of bacteria process ammonium to nitrate
http://bark214-3.berkeley.edu/MCB290/illana.htm
Anaerobic sludge digester
http://bark214-3.berkeley.edu/MCB290/illana.htm
Anaerobic methane production
Electricity sold to Seattle City Light
30% of power for the plant
We do not know the precise composition of bacteria in either the aerobic or anaerobic processes.
Plating out and culturing provides micro-organisms with a very different environment than found in the tanks
There is some hope to use new DNA/RNA identification techniques to identify bacteria and seek ways of improving processing rates
Problems!
Increased treatment capacity will be needed
What will happen in the future? A third plant will be added.
But there is resistance to expanding the processing area of existing plants although their current capacity may be exceeded
350 feet deep processor
A 350 feet deep processor is being investigated!!
Temp and O2 control systems
Recycling through biosolids application
What we do not have!
Some regulations
Seattle Biosolids Applications
The “Cornell” recommendations
What we do not have!
What we need to avoid
Giardia lamblia trophozoites, as they appear with the scanning electron microscope. Original image by Arturo Gonzalez, CINVESTAV, Mexico.
http://www.biosci.ohio-state.edu/~parasite/giardia_sem.html
The EPA breaks down land application of biosolids into 4 categories: Agricultural lands, Forest lands, Reclamation sites, and Public contact/Home lawns & gardens. Each land application category has its own set of requirements according to WAC 173-308-210, 220, 230, 240, and 250. Washington state has adapted the federal EPA rule 40 CFR 503 standards to its own rule, Chapter 173-308 WAC.
A Plain English Guide to theEPA Part 503 Biosolids Rule
http://www.epa.gov/owm/bio/503pe/
Some regulations
Class A biosolids contain no detectible levels of pathogens and and meet strict vector attraction reduction requirements and have low levels of metals. Permits are required to ensure that these standards have been met.
Different rules for different classes of biosolids.
Class B biosolids are treated but still contain detectible levels of pathogens. There are buffer requirements, public access, and crop harvesting restrictions for virtually all forms of Class B biosolids.
Class A production processes include irradiation, composting, heat drying, heat treatment, pasteurization, thermophilic aerobic digestion, and alkaline stabilization. Class A biosolids do not contain pathogens in sufficient quantity to warrant restricted access or special precautions and may be applied the same way as commercial fertilizer.
Class A Biosolids
Biosolids must be subject to one of the following four (4) time-temperature regimes: 7 percent solid or greater biosolids must be heated to 50 degrees Celsius of higher for 20 minutes or longer. 7 percent solid or greater biosolids in the form of small particles
and heated by contact with either warmed gases or immiscible liquid must be heated to 50 degrees Celsius or higher for 15 seconds or longer. Biosolids less than 7 percent solid must be heated for at least 15
seconds but less than 30 minutes using the following equation:
D=131,700,000/100.14 t Biosolids less than 7 percent solid must be heated to 50 degrees
Celsius of higher with at least 30 minutes of longer contact time.
Alternative 1: Thermally treated biosolids
There are chemical alternatives for application of alkaline
K-S Nara Paddle Dryer/Cooler
King County biosolids are anaerobically digested at the treatment plant to meet Class B pathogen reduction. Further reduction does take place after application in what King County (and other processors) refer to as a hostile environment for microbes
Class B Biosolids
In practice odor is a principal restriction to the location where Class B biosolids can be applied. This can be reduced by chemicals
Restricted Activity Site Restriction
Harvest of food crop touching ground 14 months after applicationHarvest of root crop (see next condition) 20 months after applicationHarvest of root crop if sludge on surface 38 months after applicationHarvest of other food, feed, and fiber crops 30 days after applicationGrazing of animals 30 days after applicationHarvest of turf for high contact site, 1 year after application e.g., golf course or lawn; or public access to turfAccess to sites with high potential for Restrict for 1 yearpublic exposureAccess to sites with low potential for Restrict for 30 days public exposure
EPA Class B biosolids site restrictions
Total Solids 24.8%Ammonia Nitrogen 1.2%Organic Nitrogen 5.5%Phosphorus 1.9%Potassium 0.3%Sulfur 1.1%
Biosolids Quality from the West Point Plant 2000 Average
By weight
Organic nitrogen provides a sustained release of N
West Point Plant National and State Regulatory Standards mg/kg mg/kg
Arsenic 7.07 541Cadmium 3.7 39Copper 529 1500Lead 141 300Mercury 2.71 17Molybdenum 11.1 under reconsiderationNickel 35.1 420Selenium 5.97 36Zinc 804 2800
Trace metals in West Point biosolids
Improved moisture retention
Increased growth – sometimes too much N
“Dryland” soils program
Forest Application
Reclamation
Rapid establishment of vegetation
Issues – returning to ‘natural’ vegetation may be retarded by high N
Bunker Hill Wetland, Idaho
Four arguments against biosolids application
1. Odor and ‘unpleasantness’
2. EPA is not doing its job to ensure compliance with its own regulations
3. Treatment and disposal should be local
4. Class B biosolids can cause illness to people applying them
--Limiting applications to keep soil metals low;--Testing soils before application;--Applying only at agronomic rates;--Supplying all landowners with biosolids quality
information;--Monitoring downstream water bodies and wells;--Calibrating application equipment;--Maintaining setbacks and buffers;--Avoiding application to areas prone to runoff;--Imposing access restrictions for the public.
In practice most of these items are specified in Washington State and EPA regulations
Cornell University site management recommendations
According to EPA estimates for 1993, approximately 33% of the 5.4 million dry metric tons of biosolids generated annually in the US is land applied
This is increasing due to rising costs and less available space in landfills, regulations banning ocean dumping, and a move away from incineration.
There is likely to be continued discussion as new regions consider biosolids application
Conclusion
So application to the land will increase and must be placed on a sustainable basis
ESC518, formerly MicrobialDegradation, to Bioremediation Science
Courses that deal with this topic
CIVE 484 On-Site Wastewater DisposalCIVE 482 Water and Wastewater Treatment