Tertiary Treatment: Nutrient Removal, Solids Removal, and Disinfection

Treated Wastewater Effluent Contains… BOD (biochemical oxygen demand) BOD (biochemical oxygen demand) Carbon matter, depletes O2, causes biomat growthCarbon matter, depletes O2, causes biomat growth TSS (total suspended solids) TSS (total suspended solids) Depletes O2Depletes O2 NH3 (ammonia) NH3 (ammonia) Toxic to fish, depletes O2, a nutrient that promotes biol. growthToxic to fish, depletes O2, a nutrient that promotes biol. growth NO3 (nitrate) NO3 (nitrate) Toxic to babies, drinking water regulated, a nutrientToxic to babies, drinking water regulated, a nutrient TP (total phosphorus) TP (total phosphorus) A nutrientA nutrient Pathogens (bacteria/viruses) Pathogens (bacteria/viruses) Disease causingDisease causing

First, We Must Understand Wastewater Assimilation A site’s ability to handle the amount of liquid or the amount of pollutants without causing a public health or environmental health concern A site’s ability to handle the amount of liquid or the amount of pollutants without causing a public health or environmental health concern In-ground or In-stream discharge In-ground or In-stream discharge Sometimes, high-quality effluent is necessary Sometimes, high-quality effluent is necessary Low BODLow BOD Low fecal coliformLow fecal coliform Low nutrients (Nitrogen and Phosphorus)Low nutrients (Nitrogen and Phosphorus) Protection of sensitive waterbodies, nearby… Protection of sensitive waterbodies, nearby… Or drinking water supplies (groundwater & wells)Or drinking water supplies (groundwater & wells)

“Discharge” Permits In-ground dispersal In-ground dispersal ADEM for flows of 10,000 gpd +ADEM for flows of 10,000 gpd + UIC Permit (underground injection control) UIC Permit (underground injection control) Specifies a certain effluent quantity and qualitySpecifies a certain effluent quantity and quality BOD, TSS and groundwater monitoring for NO 3BOD, TSS and groundwater monitoring for NO 3 ADPH for smaller systems ADPH for smaller systems Surface dispersal Surface dispersal Stream DischargeStream Discharge NPDES Permit (specifies BOD, TSS, NH 3, NO 3, TP, etc.) NPDES Permit (specifies BOD, TSS, NH 3, NO 3, TP, etc.) Disinfection Required Disinfection Required Spray IrrigationSpray Irrigation NPDES Permit NPDES Permit 7-10 day holding pond required 7-10 day holding pond required Disinfection Required Disinfection Required

Why is tertiary treatment needed? To better protect public health and environment To better protect public health and environment To provide additional treatment when soils or receiving waters cannot To provide additional treatment when soils or receiving waters cannot

Biological Nitrogen Removal Uptake into biological cell mass Uptake into biological cell mass Nitrification (conversion to Nitrate) Nitrification (conversion to Nitrate) Denitrification (conversion to N 2 gas) Denitrification (conversion to N 2 gas)

Biological Nitrification Conversion of Ammonia to Nitrite (Nitrosomonas) NH O 2   NO H + + H 2 O Conversion of Nitrite to Nitrate (Nitrobacter) NO O 2   NO 3 -

Nitrification (cont.) For each mg of NH 4 + converted… For each mg of NH 4 + converted… 3.96 mg of O 2 are utilized (Need Oxygen) 0.31 mg of new cells are formed 7.01 mg of alkalinity are removed

Nitrification (cont.) Nitrifying bacteria are sensitive and susceptible to a variety of conditions. Nitrifying bacteria are sensitive and susceptible to a variety of conditions. The following factors affect nitrification: The following factors affect nitrification: Conc of NH 4 + and NO 2 -Conc of NH 4 + and NO 2 - BOD/TKN ratio (BOD should be gone/removed)BOD/TKN ratio (BOD should be gone/removed) Dissolved oxygen conc (need oxygen)Dissolved oxygen conc (need oxygen) TemperatureTemperature pH (7.5 to 8.6)pH (7.5 to 8.6)

Nitrification Processes Suspended Growth Separate Stage Nitrification Single State Nitrification

Nitrification Processes Attached Growth Attached Growth Nitrification following Act. Sludge

Biological Denitrification A modification of aerobic pathways (no oxygen) A modification of aerobic pathways (no oxygen) Same bacteria that consume carbon material aerobicallySame bacteria that consume carbon material aerobically Denitrifying bacteria obtain energy from the conversion of NO 3 - to N 2 gas, but Denitrifying bacteria obtain energy from the conversion of NO 3 - to N 2 gas, but require a carbon source require a carbon source NO CH 3 OH + H 2 CO 3   C 5 H 7 O 2 N + N 2 + H 2 O + HCO 3 - NO CH 3 OH + H 2 CO 3   C 5 H 7 O 2 N + N 2 + H 2 O + HCO 3 - Organic matter Cell mass

Denitrification Need low (no) oxygen (< 1 mg/L) Need low (no) oxygen (< 1 mg/L) Need carbon source (BOD in Wastewater) Need carbon source (BOD in Wastewater) Neutral pH (pH 7) Neutral pH (pH 7) Conc of nitrate Conc of nitrate

Denitrification (cont.) Separate denitrification reactor Separate denitrification reactor or or Combined Carbon Oxidation- nitrification-denitrification reactor Combined Carbon Oxidation- nitrification-denitrification reactor A series of alternating aerobic and anoxic stagesA series of alternating aerobic and anoxic stages Reduces the amount of air neededReduces the amount of air needed No need for supplemental carbon sourceNo need for supplemental carbon source

Combined Nitrification/Denitrification (note alternating regions of aerobic and anoxic)

Phosphorus Removal Chemical Precipitation Chemical Precipitation Calcium (lime) addition at high pH (>10)Calcium (lime) addition at high pH (>10) Reacts with alkalinity Reacts with alkalinity Alum ( Aluminum Sulfate) precipitationAlum ( Aluminum Sulfate) precipitation Iron precipitationIron precipitation

Disinfection Selective destruction of disease- causing organisms Selective destruction of disease- causing organisms 1.Chlorine 2.UV Light 3.Ozone (gas)

Chlorine Disinfection 1. Liquid chlorine 2. Sodium hypochlorite (tablets) Note: not allowed to discharge chlorine (it must be removed after disinfection) * chlorine removed with either… a. sulfur dioxide a. sulfur dioxide b. sodium bisulfite b. sodium bisulfite

Tablet Chlorinator (Calcium Hypochlorite)

Chlorine Disinfection To be effective… To be effective… Chlorine concentrationChlorine concentration Contact timeContact time Proper mixingProper mixing TemperatureTemperature Number and type of organismsNumber and type of organisms

Chlorine Dose

UV Disinfection UV Light UV Light Specific wavelengths have biocidal properties (~254 nm)Specific wavelengths have biocidal properties (~254 nm) Quartz, mercury-vapor lampsQuartz, mercury-vapor lamps Cleaning requiredCleaning required No residualNo residual

UV Disinfection a specific wavelength of light

UV Disinfection

Ozone Disinfection O 3 a gas, must be generated on-site O 3 a gas, must be generated on-site Bubbled into a basin (or pipeline) with treated effluent Bubbled into a basin (or pipeline) with treated effluent Great disinfectant! Great disinfectant! No residual…ozone degrades to oxygen, O 2 No residual…ozone degrades to oxygen, O 2 Costs More, Need equipment and electricity Costs More, Need equipment and electricity

Ozone Disinfection Flow Diagram Ozone Generation