ENV H 440ENV H 541 Wastewater treatment processes

ENV H 440/ENV H 541 Wastewater treatment processes (I) John Scott Meschke Gwy-Am Shin Office: Suite 2249, Office: Suite 2339, 4225 Roosevelt Phone: 206 -221 -5470 Phone: 206 -543 -9026 Email: jmeschke@u. washington. edu Email: gwyam@u. washington. edu

Key points • • Purpose of the individual unit processes The typical operating conditions The outcome of the processes Microbial reduction of the processes

How much wastewater do we produce each day? These values are rough estimates only and vary greatly by locale. Wastewater Characteristics

Wastewater treatment systems • Decentralized – Septic tank – Waste stabilization ponds • Facultative lagoon • Maturation lagoon – Land treatment – Constructed wetland • Centralized

Sewer systems

Typical composition of untreated domestic wastewater

Microorganism concentrations in untreated wastewater

(Minimum) Goals of wastewater treatment plants • <30 mg/L BOD 5 • <30 mg/L of suspended solids • <200 CFU/100 m. L fecal coliforms

Conventional Community (Centralized) Sewage Treatment Secondary Treatment Using Activated Sludge Process Pathogen Reductions Vary from: low (<90%) to Very High (>99. 99+%) Sludge drying bed or mechanical dewatering process

Typical Municipal Wastewater Treatment System Preliminary or Pre- Primary Treatment Sludge Treatment & Disposal Secondary Treatment Disinfection

Preliminary Wastewater Treatment System Preliminary or Pre. Treatment Solids to Landfill

Preliminary Treatment - Bar Racks: are used to remove large objects that could potentially damage downstream treatment/pumping facilities. Ref: Metcalf & Eddy, 1991 Preliminary Treatment Facilities

Preliminary Treatment - Grit chamber: used to remove small to medium sized, dense objects such as sand, broken glass, bone fragments, pebbles, etc.

Primary Wastewater Treatment Primary Treatment

Primary sedimentation • To remove settleable solids from wastewater

Primary Clarification Scum: Oil, Grease, Floatable Solids Primary Effluent Primary Sludge Influent from Preliminary Treatment Section through a Circular Primary Clarifier Primary Treatment

Primary sedimentation • • To remove settleable solids from wastewater Maximum flow: 30 - 40 m 3 per day Retention period: 1. 5 - 2. 0 hours (at maximum flow) 50 - 70 % removal of suspended solids 25 - 35 % removal of BOD 5 ~20 % removal of phosphate ~50 % removal of viruses, bacteria, and protozoa 90 % removal of helminth ova

Secondary Wastewater Treatment Secondary Treatment

Secondary treatment processes • To remove suspended solids, nitrogen, and phosphate • 90 % removal of SS and BOD 5 • Various technologies – Activated sludge process – Tricking filter – Stabilization ponds

Secondary Treatment Using Activated Sludge Process Sludge drying bed or mechanical dewatering process Secondary Treatment

Simplified Activated Sludge Description The Activated Sludge Process Aerobic microbes utilities carbon and other nutrients to form a healthy activated sludge The biomass floc is allowed to settle out in the next reactor; some of the AS is Treatment Secondary

General Microbial Growth • • Carbon Source: Dissolved organic matter Energy Source: Dissolved organic matter Terminal Electron Acceptor: Oxygen Nutrients: Nitrogen, Phosphorus, Trace Metals • Microorganisms: Indigenous in wastewater, recycled from secondary clarifier Secondary Treatment

Activated Sludge Aeration Basins Empty basin, air diffusers on bottom Same basin, in operation Secondary Treatment

The Oxidation Ditch Ref: Reynolds & Richards, 1996, Unit Operations and Processes in Environmental Engineering Secondary Treatment

The Oxidation Ditch Ref: Reynolds & Richards, 1996, Unit Operations and Processes in Environmental Engineering Secondary Treatment

Circular Secondary Clarifier Secondary Effluent Return (Secondary) Sludge Line Influent from Activated Sludge Aeration Basin or Trickling Filter Section through a Circular Secondary Clarifier Secondary Treatment

Activated Sludge Floc Ref: Brock, Madigan, et al, Biology of Microorganisms This is a picture of the biological flocs formed in the activated sludge aeration basin. These flocs must settle out and be removed in the secondary clarifier. Secondary Treatment

Activated Sludge - Problem Microorganisms Ref: Brock, Madigan, et al, Biology of Microorganisms The growth of filamentous micro -organisms in activated sludge systems is common. These microorganisms make the biological flocs extremely hard to settle and can cause foaming in the aeration basin. Filamentous organisms are strict aerobes and cannot compete for substrate except under aerobic conditions. By creating anaerobic or anoxic conditions at the influent end of the aeration basin, filamentous organisms are effectively “starved” and do not proliferate. This is called using ‘biological selectors’ in the treatment process. Secondary Treatment

Activated sludge process • To remove suspended solids, nitrogen, and phosphate • 90 % removal of BOD 5 • Food to microorganism ratio (F: M ratio): 0. 25 kg BOD 5 per kg MLSS (mixed liquor suspended solids) per day at 10 o. C or 0. 4 kg BOD 5 per kg MLSS per day at 20 o. C • Residence time: 2 days for high F: M ratio, 10 days or more for low F: M ratio • Optimum nutrient ratio: BOD 5: N: P =>100: 5: 1 • ~20 % removal of phosphate • > 90 % removal of viruses and protozoa and 45 - 95 % removal of bacteria

Secondary Treatment Using Trickling Filter Process Trickling Filter Secondary Treatment

Trickling Filter Primary effluent drips onto rock or man-made media Rotating arm to distribute water evenly over filter Rock-bed with slimy (biofilm) bacterial growth Treated waste to secondary clarifier Primary effluent pumped in http: //www. rpi. edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/streem/trickfil. jpg

Trickling Filter http: //www. eng. uc. edu/friendsalumni/research/labsresearch/biofilmreslab/Tricklingfilter_big. jpg

Tricking filter process • To remove suspended solids, nitrogen, and phosphate • 90 % removal of BOD 5 • Organic loading (BOD 5 X flow/volume of filter): 0. 1 kg BOD 5 per m 3 per day • Hydraulic loading: 0. 4 m 3 per day per m 3 of plan area • ~20 % removal of phosphate • Variable removal levels of viruses, 20 -80 % removal of bacteria and > 90 % removal of protozoa

Stabilization Ponds • The oldest wastewater treatment systems – Requires a minimum of technology – Relatively low in cost – Popular in developing countries and small communities in the US (90 % communities with population <10, 000) • Used for raw sewage as well as primary‑ or secondary‑treated effluents. • Facultative ponds and aerated Ponds and Lagoons

Facultative Ponds and Lagoons

Facultative ponds • Facultative ponds: upper photic (aerobic) zone, facultative (aerobic and anaerobic) zone and lower anaerobic zone. – Upper aerobic zone: algae use CO 2, sunlight and inorganic nutrients (photosynthesis) to produce oxygen and algal biomass. – Facultative zone: bacteria and other heterotrophs convert organic matter to carbon dioxide, inorganic nutrients, water and microbial biomass. – Lower anaerobic zone: anaerobic bacteria degrade the biomass from upper zones • Influence by many factors – – – Sunlight Temperature p. H Biological activities Characteristics of wastewater Ponds and Lagoons

Facultative ponds • To remove suspended solids, nitrogen, phosphate, and pathogens • Operating water depth: 1 -2. 5 meters • (maximum) BOD loading: 2. 2 -5. 6 g/m 3 /day • Retention time: 3 -6 months • >90 % BOD removal (warm and sunny climates) • Microbe removal may be quite variable depending upon pond design, operating conditions and climate. – 90 -99% removal of indicator and pathogenic bacteria – 99 % removal of PV 1 – 99. 9 reduction of Giardia and Cryptosporidium

Aerated Lagoons Stabilization Lagoon Aerated Lagoons http: //www. lagoonsonline. com/marshill. htm Ponds and Lagoons

Aerated lagoons • Biological activity is provided by mainly aerobic bacteria • Influence by many factors – Aeration time – Temperature – p. H – Biological activity – Characteristics of wastewater

Aerated lagoons • To remove suspended solids, nitrogen, phosphate, and pathogens • Operating water depth: 1 -2 meters • Retention time: <10 days • 85% BOD removal (at 20 o. C and an aeration period of 5 days) • 65% BOD removal (at 10 o. C and an aeration period of 5 days) • Microbe removal may be quite variable depending upon pond design, operating conditions and climate

Wastewater Disinfection

Typical Municipal Wastewater Treatment System Preliminary or Pre- Primary Treatment Sludge Treatment & Disposal Secondary Treatment Disinfection

Sludge processing • • Thickening Digestion Dewatering Disposal

Sludge thickening • To reduce the volume of sludge – to increase sludge solids at least 4 % • Gravity thickening and mechanical thickening • Gravity thickening – loading rate: 30 -60 kg/m 2 per day • Mechanical thickening – dissolved air flotation, gravity belt thickeners, and centrifuge thickening – loading rate: 10 -20 kg/m 2 per day (dissolved air flotation), 4001000 L/m (gravity belt thickeners), 1500 -2300 L/m (centrifuge thickening) • The concentration of pathogens increased during this process

Regulatory requirement for disposal of sewage sludge • Class B biosolids – < 2 milion MPN/g of fecal coliforms – Seven samples over 2 -wweks period – ~2 log removal • Class A biosolids – – – < 1000 MPN/g of fecal coliforms < 3 MPN/4 g of Salmonella sp. < 1 PFU/4 g of enteric viruses < 1/4 g of Helminth ova ~ 5 log removal

Processses to significantly reduce pathogens (PSRP) for a Class B biosolids • • • Aerobic digestion Anaerobic digestion Air drying Composting Lime stabilization

Digestion • To stabilize organic matter, control orders, and destroy pathogens • Aerobic digestion and anaerobic digestion • Aerobic digestion – loading rate (maximum): 640 g/m 2 per day – Temperature and retention time: 68 o. F for 40 days or 58 o. F for 60 days – Solids and BOD reduction: 30 -50 % – < 2. 5 % solids

Anaerobic digestion • Operation conditions (optimum) – – – Temperature: 85 -99 o. F (98 o. F) p. H: 6. 7 -7. 4 (7. 0 -7. 1) Alkalinity: 2000 -3500 mg/L Solid loading: 0. 02 -0. 05 lb/ft 3/day Retention time: 30 -90 days • Treatment outcome – Solid reduction: 50 -70 % – Gas production: methane and carbon dioxide – Significant reduction of most pathogens

Processses to further reduce pathogens (PFRP) for a Class A biosolids • Heat drying • Thermophilc aerobic digestion – 132 -149 o. F for 4 -20 hours • Pasturization – 158 o. F for 30 minutes • Beta- or gamma ray irradiation – > 1. 0 Mrad at room temperature

Dewatering • To concentrate sludge by removing water • Pressure filtration, centrifugation, and screw press • Pressure filtration (belt filter press and plate-andframe filter) – Usually with polymer floccuration – Loading rate: 40 -60 gpm/m (hydroulic) and 500 -1000 lb/m/h (solid) – Feed solid: 1 -6 % – Cake solids: 15 -30 %

Disposal • • Land application Landfill Incineration Ocean dumping (no longer allowed in US)