waste treatment envr 421 mark sobsey. household human wastes and wastewaters

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Waste Treatment ENVR 421 Mark Sobsey Slide 2 Household Human Wastes and Wastewaters Slide 3 Excreta and Graywater Definitions and Properties Excreta: Human feces and urine Managed in different ways: Direct disposal on land or in water Direct use as fertilizer, soil conditioner and for aquaculture Pre-treatment prior to use Dilution with water to convey (sewage) for disposal or use Direct use of untreated (raw) sewage Treatment and discharge to land or water Treatment and reuse (agriculture, aquaculture, horticulture, industrial and civil use Graywater: Other wastewater from human activity Not directly from human fecs and urine Wastewater from washing, bathing, etc Contains human wastes and exudates Slide 4 Managing Human Excreta - Options Dry Collection: Open defecation Collect in a container e.g., chamber pot Discharge to the environment w/ or w/o Rx Latrines several kinds Treat or dispose of or both Separate feces and urine; Then, treat/store, use, dispose to the environment Slide 5 Managing Human Excreta - Options Semi-wet (or semi-dry) Use some water Pour-flush toilets and other low water use systems Slide 6 Managing Human Excreta - Options Wet Systems On-site Septic Systems Other On-site systems Soak pits Sewerage Sewage treatment systems Slide 7 Human Excreta Resource or Risk? Nitrogen (N)4.5 Phosphorous (P)0.6 Potassium1.0 Organic matter (as BOD) 35 Human excreta as a potential resource Contains nutrients (N, P, K, and organic matter) Nutrients and organic matter are: Detrimental in water, esp. surface water Eutrophication, anoxia, fish kills Beneficial on land Fertilizer, soil conditioner, land stabilizer Widely used as a fertilizer and soil amendment in both developed and developing countries Potential for excreta misuse and environmental pollution is great without proper attention to management plans and human behavior considerations Annual Amounts/Person, Kg Slide 8 Nutrient Content of Human Excreta Rich source of inorganic plant nutrients: N, P K and organic matter Daily human excretion: ~30 g of C (90 g of organic matter), ~ 10-12 g N, ~ 2 g of P and 3 g of K. Most organic matter in feces most N and P (70-80 %) in urine. K equally distributed between urine and feces. Slide 9 Organics kg COD/ (Personyear) 12.3 3.6 14.1 Volume Liter / (Personyear) 10.000 200.000 l 500 l 50 l source: Otterpohl Nutrient content kg N,P,K / (Personyear) N P K 0.8 5.3 1.0 Composition of Household Waste and Wastewater greywaterurine faeces Slide 10 of no major (or less) hygienic concern/risk volumetrically the largest portion of wastewater contains almost no (or less) nutrients (simpler treatment) may contain spent washing powders etc. 3. greywater less hygienically critical (less risk) contains the largest proportion of nutrients available to plants may contain hormones or medical residues 2. urine hygienically critical (high risk) consists of organics, nutrients and trace elements improves soil quality and increase its water retention capacity 1. feces characteristicfraction Characteristics of Human Wastes Slide 11 source: Drangert, 1998 Fertilizer Potential of Human Excreta Slide 12 treatment utilisation substances faeces (brownwater) anaerobic digestion, drying, composting biogas, soil improvement constructed wetlands, gardening, wastewater ponds, biol. treatment, membrane- technology greywater (shower, washing, etc.) irrigation, groundwater- recharge or direct reuse urine (yellowwater) liquid or dry fertiliser hygienisation by storage or drying Options for Excreta and Greywater Utilization Slide 13 Wastewater Impacts to Natural Receiving Waters Treated wastewater is often discharged to nearby natural waters BOD Chemicals (N,P) Synthetic Chemicals Antibiotics Microbial Pathogens Conventional Wastewater Treatment Developed World Slide 14 Water Use Cycle Water Source Water Treatment Plant Water Distribution System Water Use Wastewater Collection Wastewater Treatment Plant Discharge to Receiving Water Slide 15 Pathogen Concentrations in Raw Sewage Highly variable and influenced by many factors: Types and prevalence of enteric infections in the population Geographic, seasonal, and climatological factors "Strength" and age of the sewage. More water use, weaker sewage. "Guesstimated Worst-case" Pathogen Concentrations in U.S. Raw Sewage (No./L): Enteric Viruses and Protozoan Cysts: ~ 10,000 of Each Group/Liter. Enteric Bacteria: ~100,000/Liter. Slide 16 Municipal Wastewater Collection (Chapel Hill, NC) Generally, a gravity flow system Includes pump stations and Force Main sewers Slide 17 Conventional Sewage Treatment Slide 18 Primary TreatmentSecondary TreatmentTertiary Treatment Anaerobic Digestion Slide 19 Trickling Filter and Aeration Basin for Wastewater Treatment Slide 20 Treating Separated Sewage Solids or Sludge Slide 21 Waste Solids (Sludge) Treatment Treatment of the settled solids from 1 o and 2 o sewage treatment Biological digestion to biologically stabilize the sludge solids Anaerobic digestion (anaerobic biodegradation) Aerobic digestion (aerobic biodegradation) Mesophilic digestion: ambient temp. to ~40 o C; 3-6 weeks Thermophilic digestion: 40-60 o C; 2-3 weeks Produce digested (biologically stabilized) sludge solids for further treatment and/or disposal Waste liquids from sludge treatment are recycled through the sewage treatment plant Waste gases from sludge treatment are released (or burned if from anaerobic digestion: methane, hydrogen, etc.) Slide 22 Processes to Further Reduce Pathogens PFRP: Class A Sludge Class A sludge: Enteric Microbe/Pathogen Reductions by Sludge Treatment Processes Anaerobic and aerobic digestion processes Moderate reductions (90-99%) by mesophilic processes High reductions (>99%) by thermophilic processes Thermal processes Reductions depend on temperature Greater reductions at higher temperatures Temperatures >55 o C usually produce appreciable pathogen reductions. Alkaline processes: lime or other alkaline material Reductions depend on pH; greater reductions at higher pHs pH >11 produces extensive pathogen reductions Composting: high temperature, aerobic biological process Reductions extensive (>99.99%) when temperatures high and waste uniformly exposed to high temperature Drying and curing Variable and often only moderate pathogen reductions Slide 33 Processes to Further Reduce Pathogens PFRP: Class A Sludge Class A sludge:


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