Chapter 7 - Fundamentals of Biological Treatment

7-1. Overview of Biological wastewater Treatment

Overview of Biological wastewater Treatment Objectives of biological treatment Some useful definitions Role of microorganisms in wastewater treatment Type of biological process for wastewater treatment Suspended growth processes Attached growth processes

Objectives of Biological Treatment To transform dissolved and particulate biodegradable constituents into acceptable end products. To capture and incorporate suspended and nonsettleable colloidal solids into a biological floc or biofilm. To transform or remove nutrients. (such as nitrogen and phosphorus) To remove specific trace organic constituents and compounds.

Objectives of Biological Treatment Influent Bar rack Screenings Grit chamber Grit Primary clarifier Sludge Aeration tanks Waste sludge (optional) Secondary clarifier Disinfection Effluent Return activated sludge Waste sludge (optional) a b Aerated lagoon Settling pond Return sludge (optional) Figure 1. Typical (simplified) flow diagrams for biological used for wastewater treatment (a) activated-sludge process, (b) aerated lagoons

Objectives of Biological Treatment Figure 1. Typical (simplified) flow diagrams for biological used for wastewater treatment (c) trickling filter, (d) rotating biological contactors. Influent Bar rack Screenings Grit chamber Grit Primary clarifier Sludge Trickling filter Waste sludge (optional) Secondary clarifier Disinfection Effluent c Recycle chamber Primary clarifier Aeration tanks Secondary d

Some useful definitions Treatment functions Biological nutrient removal(BNR) Stabilization Nitrification Biological phosphorus removal Denitrification Carbonaceous BOD removal Substrate Some useful terms. Metabolic function Aerobic process Anaerobic process Anoxic process Facultative process Combined process Treatment process Suspended growth process Attached growth process Lagoon process

Biological Treatment Metabolic function Term Definition Table 1. definition of common terminology used for biological wastewater treatment Term Definition Metabolic function Aerobic (oxic) process Biological treatment process that occur in the presence of oxygen Anaerobic process The process that occur in the absence of oxygen Anoxic process Nitrate nitrogen is converted biologically to nitrogen gas in the absence of oxygen, Known as denitrification Facultative process Process in which the organisms can function in the presence or absence of molecular oxygen Combined aerobic/ Anoxic/Anaerobic process Various combinations of aerobic, anoxic, and anaerobic processes grouped together to achieve a specific treatment objective

Biological Treatment Treatment processes Term Definition Table 1. definition of common terminology used for biological wastewater treatment Term Definition Treatment processes Suspended-growth processes Biological treatment processes in which the microorganisms responsible for the conversion of the organic matter or other constituents in the wastewater to gases and cell tissue are maintained suspension within the liquid Attached-growth Biological treatment processes in which the microorganisms responsible for the conversion of the organic matter or other constituents in the wastewater to gases and cell tissue are attached to some inert medium, such as rock, slag, or specially designed ceramic or plastic materials. Also known as fixed-film processes Combined processes Term used to describe combined processes (combined suspended and attached growth processes) Lagoon processes A generic term applied to treatment processes that take place in pond or lagoons

Biological Treatment Treatment functions Term Definition Table 1. definition of common terminology used for biological wastewater treatment Term Definition Treatment functions The term applied to the removal of nitrogen and phosphorus in biological treatment Biological phosphorus removal Removal of phosphorus by accumulation in biomass and subsequent solids separation Carbonaceous BOD removal Conversion of the carbonaceous organic matter to cell tissue and various gaseous end product. Assumed – Nitrogen converted to ammonia Nitrification Ammonia is converted first to nitrite and then to nitrate Denitrification Nitrate is reduced to nitrogen and other gaseous Stabilization The biological process by sludge from primary settling and wastewater is stabilized. The process is known as aerobic or anaerobic digestion. Substrate The organic matter or nutrients that are converted during biological treatment or that may be limiting in biological treatment

Role of microorganism in wastewater treatment Removal of dissolved and particulate BOD and the stablization of organic matter found in wastewater. Conversion of simple end product and additional biomass v1(organic material) + v2O2 + v3NH3 + v4PO43- → v5(new cells) + v6CO2 + v7H2O v : the stoichometric coefficient O2, NH3, PO43- : Nutrients needs for the conversion of the organic matter to simple end products(CO2)

Role of microorganism in wastewater treatment Nitrogen removal in the wastewater treatment process. Nitrification Denitrification Phosphorus removal in the wastewater treatment process. Excess inorganic phosphorus ingestion and storage of microorganisms.

Types of biological process for wastewater treatment Suspended growth process. Attached growth process. Typical process applications are given in table 2

Wastewater Treatment Table 2. major biological treatment processes used for wastewater treatment Type Common name Use Aerobic processes Suspended growth Activated-sludge process Aerated lagoons Aerobic digestion C - BOD removal, nitrification C - BOD removal, stabilization Attached growth Trickling filters Rotating biological contactors Packed-bed reactors hybrid (combined) suspended and attached growth processes Trickling filter / activated sludge

Wastewater Treatment Table 2. major biological treatment processes used for wastewater treatment Type Common name Use Anoxic processes Suspended growth Suspended growth denitrification denitrification Attached growth Attached growth denitrification Anaerobic processes suspended growth Anaerobic contact processes Anaerobic digestion C – BOD removal Stabilization, solids destruction, pathogen kill Anaerobic packed and fluidized bed C – BOD removal, waste stabilization, denitrification sludge blanket Up flow anaerobic sludge blanket C – BOD removal, especially high strength wastes hybrid Up flow sludge blanket / attached growth

Suspended growth process The microorganisms are maintained by appropriate mixing method. The most common suspended growth process is the activated sludge process. Influent Effluent Return activated sludge Air Plug flow aeration tank Clarifier Sludge Complete mix aeration tank Figure 2. Suspended growth biological treatment process

Attached growth process The microorganisms are attached to an inert packing material. Packing material Rock · Gravel Slag · Sand Redwood · Plastic Synthetic materials The organic materials and nutrients are removed from the wastewater flowing past the attached growth also known as a biofilm. The most aerobic attached growth process : trickling filter.

Attached growth process Effluent Clarifier Sludge Influent Recycle (optional) Trickling filter with rock packing Tower trickling filter with plastic packing Recycle Figure 3. Attached growth biological treatment process