CEE 370: Lecture #8 - Rowan University

CEE 370: Lecture #8 - Rowan University

Wastewater Treatment Municipal WW Management Systems Sources of Wastewater Transmission and Pumping Processing at the Source Treatment

Wastewater Collection Reuse/Disposal Sources & Types of WW Domestic Wastewater from residences, commercial & institutional flows ~70-90% of water supplied Industrial Wastewater

highly dependent on industry Infliltration/Inflow enters through leaks, foundation drains, etc. Stormwater for combined sewers - largely in older cities Typical WW Characteristics Parameter

Conc. BOD TSS COD Ammonia TOC Chloride 250 mg/L 250 mg/L 500 mg/L 30 mg/L 100 mg/L + 50 mg/L

1972: Federal Water Pollution Control Act PL 92-500 subsequently amended and now called the Clean Water Act established water quality goals fishable & swimmable and timetable established National Pollution Discharge Elimination System (NPDES) construction grants for WW treatment required secondary treatment (30/30)

30 mg/L BOD5 30 mg/L TSS Conventional WW Treatment Preliminary Treatment Secondary Sedimentation Primary Sedimentation Biological Process

Sludge Disinfection Sludge Preliminary Treatment To remove materials that will interfere with subsequent treatment

Coarse Screening (bar racks) Medium Screening Comminution Flow measuring Pumping Grit removal Pre-aeration Bar Racks

Metal bars spaced a few cm apart across water flow mechanical or manually cleaned size of unit set by approach velocity 0.6-1.0 m/s for mechanically cleaned 0.3-0.7 m/s for manually cleaned see Fig 10.4 and example 10.2 on pg. 311 Grit Removal

Grit chambers intended to remove sand, cinders, gravel that may enter system by cracks in pipes, inflow etc. Grit can cause excess wear in pipes and pumps small sedimentation tanks; designed with the help of Stokes Law no organics removal

Grit Chamber Primary Sedimentation Purpose: to remove suspended solids (smaller than grit, and less harmful) Typical efficiency 67% TSS removal 33% BOD removal

Design parameters overflow rate weir loading rate detention time Primary effluent is largely composed of soluble and colloidal organics which can be converted to settleable microbial solids and CO2 by biological treatment

Primary Sedimentation Primary Treatment Removes ~50% of suspended solids Parameter Design Range Typical Value Overflow Rate 35-45 m/d 800-1200 gal/ft2/d

40 m/d 1000 gal/ft2/d Detention Time 1.5-2.5 h 2h 2 2 125-500 m /d

275 m /d Weir loading 10,000-40,000 gal/ft/d 20,000 gal/ft/d rate Primary Sed. Tank Primary Clarifier: Center Feed Secondary Treatment

Generally includes some biological process plus secondary clarification Required under PL92-500 Converts soluble and colloidal organic materials to biomass and CO2 Biological Treatment Suspended Growth Activated Sludge Conventional, Extended Aeration, Contact Stabilization

Aerated lagoons Aerobic digestion Attached Growth Trickling Filters Rotating Biological Contactors Suspended Growth Systems Air Aeration Tank Return Activated Sludge

Secondary Sedimentation Sludge Waste Activated Sludge Attached Growth: Trickling Filters Rotary Distributor Rocks or Plastic Media Air Underdrain

With rocks, depth is limited to 2-3 m because of oxygen needs Rotating Biological Contactors Drum diameters are typically 10-12 ft. Rotation speed: ~1.5 rpm May be in several stages No flow recycle Requires piloting

Secondary Clarifier Sludge Disposal Thickening gravity, flotation Digestion aerobic, anaerobic

Mechanical Dewatering Vacuum filtration, centrifugation, pressure filtr. Disposal land application, burial, incineration Anaerobic Digestion Sludge held without aeration for 10-90 days Process can be accelerated by heating to 35-40oC These are called High Rate Digestors (10-20 days) Advantages low solids production

useable methane gas produced Disadvantages high capital costs susceptibility to shocks and overloads Sludge Dewatering Sludge drying beds historically the most common sand bed, 15-30 days, evaporation & seepage Vacuum Filtration

cylindrical rotating drum covered with fabric submerged with applied vacuum Continuous belt filter presses (follows) Plate pressure filters vertical plates mounted on a frame Belt Filter Press (Komline-Sanderson)

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