Water and wastewater treatment processes ENV H 452/ENV H 542 John Scott Meschke Office: Suite 2249, 4225 Roosevelt Phone: Gwy-Am Shin Office: Suite 2339, 4225 Roosevelt Phone:

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

Wastewater treatment processes

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

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

Sewer systems

Typical composition of untreated domestic wastewater

Microorganism concentrations in untreated wastewater

(Minimum) Goals of wastewater treatment processes <30 mg/L BOD 5 <30 mg/L of suspended solids <200 CFU/100ml fecal coliforms

Conventional Community (Centralized) Sewage Treatment Pathogen Reductions Vary from: low ( %) Secondary Treatment Using Activated Sludge Process Sludge drying bed or mechanical dewatering process

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

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

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

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

Primary sedimentation To remove settleable solids from wastewater Maximum flow: m 3 per day Retention period: hours (at maximum flow) % removal of suspended solids % 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 –Aerated lagoons –Rotating biological contractors

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

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

Activated sludge process To remove suspended solids, nitrogen, and phosphate 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 90 % removal of BOD 5 and SS ~20 % removal of phosphate >90 % removal of viruses and protozoa and % removal of bacteria

Secondary Treatment Using Trickling Filter Process 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 Primary effluent pumped in Treated waste to secondary clarifier

Trickling Filter

Tricking filter process To remove suspended solids, nitrogen, and phosphate 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 90 % removal of BOD 5 and SS ~20 % removal of phosphate Variable removal levels of viruses, % removal of bacteria and >90 % removal of protozoa

Wastewater Disinfection Disinfection

Wastewater disinfection To inactivate pathogens in wastewater Several choices –Free chlorine and combined chlorine –UV –Ozone –Chlorine dioxide

Overall pathogen reduction in wastewater treatment

Water treatment processes

Water contaminants Chemicals –Inorganics –Organics Synthetic organic compounds Volatile organic compounds Microbes –Viruses –Bacteria –Protozoa parasites –Algae –Helminths

Water contaminants (I)

Water contaminants (II)

Water contaminants (III)

Water contaminants (IV)

Water contaminants (V)

Multiple barrier concept for public health protection

Barrier Approach to Protect Public Health in Drinking Water Source Water Protection Treatment Technology Disinfection Disinfectant residual in distribution system

Water treatment processes

Oxidation To remove inorganics (Fe ++, Mn ++ ) and some synthetic organics –Cause unaesthetic conditions (brown color) –Promote the growth of autotrophic bacteria (iron bacteria): taste and order problem Free chlorine, chlorine dioxide, ozone, potassium permanganate –Fe ++ + Mn ++ + oxygen + free chlorine → FeO x ↓ (ferric oxides) + MnO 2 ↓ (manganese dioxide) –Fe (HCO 3 ) 2 (Ferrous bicarbonate) + KMnO 4 (Potassium permanganase) → Fe (OH) 3 ↓ (Ferric hydroxide) + MnO 2 ↓ (manganese dioxide) –Mn (HCO 3 ) 2 (Manganese bicarbonate) + KMnO 4 (Potassuim permanganase) → MnO 2 ↓ (manganese dioxide)

Physico-chemical processes To remove particles in water Coagulation/flocculation/sedimentation Filtration

Rapid Mix Intense mixing of coagulant and other chemicals with the water Generally performed with mechanical mixers Chemical Coagulant

Major Coagulants Hydrolyzing metal salts –Alum (Al 2 (SO 4 ) 3 ) –Ferric chloride (FeCl 3 ) Organic polymers (polyelectrolytes)

Coagulation with Metal Salts Al(OH) Al x (OH) y Colloid Al(OH) 3 Colloid Al(OH) 3 Colloid + + Soluble Hydrolysis Species (Low Alum Dose) Colloid Al(OH) 3 (High Alum Dose) Floc Sweep Coagulation Charge Neutralization

Horizontal Paddle Flocculator

Flocculation Example Water coming from rapid mix. rapid mix. Water goes to sedimentation basin. basin.

Sedimentation Basin

Sedimentation Basin Example Water coming from flocculation basin. Water goes to filter. Floc (sludge) collected in hopper Sludge to solids treatment

Coagulation/flocculation/and sedimentation To remove particulates and natural organic materials in water Coagulation – mg/L of Alum at pH (sweep coagulation) –rapid mixing: G values = /second Flocculation: –Slow mixing: G values = 30-70/second –Residence time: minutes Sedimentation –Surface loading: gpm/ft 2 –Residence time: 1 – 2 hours Removal of suspended solids and turbidity: % Reduction of microbes –74-97 % Total coliform –76-83 % of fecal coliform –88-95 % of Enteric viruses –58-99 % of Giardia –90 % of Cryptosporidium

Filtration To remove particles and floc that do not settle by gravity in sedimentation process Types of granular media –Sand –Sand + anthracite –Granular activated carbon Media depth ranges from 24 to 72 inches

Filter Example Water coming from sedimentation basin. AnthraciteSand Gravel (support media) Water going to disinfection

Mechanisms Involved in Filtration Interception: hits & sticks Sedimentation: quiescent, settles, & attaches Flocculation: Floc gets larger within filter Entrapment: large floc gets trapped in space between particles Floc particles Granular media, e.g., grain of sand Removal of bacteria, viruses and protozoa by a granular media filter requires water to be coagulated

Rapid filtration To remove particulates in water Flow rate: 2-4 gpm/ft 2 Turbidity: < 0.5 NTU (often times < 0.1 NTU) Reduction of microbes –50-98 % Total coliform –50-98 % of fecal coliform –10-99 % of enteric viruses – % of Giardia –99 % of Cryptosporidium

Disinfection in water To inactivate pathogens in water Various types –Free chlorine –Chloramines –Chlorine dioxide –Ozone –UV

Trend in disinfectant use (USA, % values) Disinfectant Chlorine gas NaClO 2 (bulk) NaClO 2 (on- site) 002 Chlorine dioxide Ozone Chloramines

Comparison of major disinfectants ConsiderationDisinfectants Cl 2 ClO 2 O3O3 NH 2 Cl Oxidation potential StrongStronger?StrongestWeak ResidualsYesNo Yes Mode of action Proteins/ NA Proteins Disinfecting efficacy GoodVery goodExcellentModerate By-productsYes Yes?No