Biological Wastewater Treatment
Advantages of using commercial formulated bacteria products..Bioaugmentation
Biological degradation is a naturally occurring process through which organic materials such as leaves, animal wastes, and natural chemical substances are utilised by various microorganisms to create additional cell mass with carbon dioxide, water, and nitrogenous compounds as by-products. Man has developed systems to use naturally occurring microbes to neutralise his own potentially polluting wastes from domestic and industrial sources.
1.1 Types of Biological Treatment
Among the different types of biological systems used to treat organic waste water are activated sludge plants, aerated lagoons, and various types of fixed film reactors. Several different types of fixed film reactors include trickling filters, rotating biological contactors, and immobilised columns.
1.2 Organisms
The bacteria in waste water treatment systems remove soluble and particulate organic food matter and convert it into new cell growth and by-products. They are considered to be primary decomposers. While a large number of different kinds of microbial organisms are capable of degrading organic materials, the types used in wastewater treatment systems are chosen, not only based on their ability to use organics, but also on their ability to settle after the degradation process is completed. Single cell bacterial organisms and certain type of protozoa are capable of clumping together, forming a floc (Bio-coagulation) which settles easily thus creating clear supernatant. Filamentous bacteria and fungi which are light weight, have a large surface area and are poor settlers and very commonly causing bulking in aeration basins and subsequently in clarifiers.
Thus, the importance of bacterial activities in activated sludge systems:
biodegradation of soluble substances.
bio-coagulation of TSS i.e. separation of sludge and supernatant.
1.3 Degradation Process
Three stages of biodegradation occur simultaneously in a wastewater treatment plant. Transfer is the process by which organic matter comes in contact with the organisms. Through absorption, dissolved organic material is transported into the cell to be used as a food source. Through adsorption, the bacteria attach to large colloidal particles, and using secreted enzymes, chemically break them into particles small enough to be transported into their cells.
This process of producing certain types of enzymes and biosurfactants is important especially in wastewater with high percentage of complex organic compounds which have poor solubility. Very commonly white foam formation is noticed in aeration basins upon seeding via activation unit as biosurfactant is being induced to breakdown complex chemicals e.g. hydrocarbon compounds.
Conversion is the process by which the bacterial cell metabolises its food. Stabilization occurs when the organisms are full and their activity has decreased. Cells in this stage settle or flocculate easily.
1.4 Activated Sludge Process
1.4.1 Introduction
The objective of wastewater treatment is to remove dissolved organic matter and reduce the amount of suspended organic matter present in a given wastewater stream. After treatment of wastewater the supernatant separated in an efficient clarifier can be discharged into a receiving stream with little or no adverse effect. This can be monitored based on the BOD/COD reading.
Biological wastewater treatment utilises microorganisms, particularly bacteria, to degrade both dissolved organics & inorganics and reduce suspended organic matter. Products have been developed utilising formulated naturally occurring microbes to neutralise potentially polluting wastewaters from specific industrial sources.
The bacteria remove soluble and particulate organic matter and convert it into new cell growth and by-products (CO2 + H2O + NH3 + NO3 + SO4 + Biomass).
Bacteria are capable of clumping together, forming a floc which settles easily.
Lightweight microorganisms, such as filamentous bacteria and fungi, have large surface area and are poor settlers.
Commercial formulated products are easily dosed and can be applied when needed especially during high organic/inorganic loading in aeration tanks, thus giving a consistent COD reading for the final discharge.
1.5 Overcoming Problems
The bacteria in a biological waste treatment system can be shocked in a number of ways. Foremost among these is elevated BOD/COD which occurs with organic overloading. In this case, the bacteria in the system are not sufficiently numerous to consume all of the food available. Loading of this type may also be fatal to the bacteria if the material is toxic to the organisms. When this shock loading occurs, commercial bacteria formulations may be added to increase the number of organisms consuming the BOD/COD or to replace organisms which have been killed during a toxic spill, thus stabilising the F:M (Food : Microorganism ratio). During cold or extremely high temperature weather, bacterial metabolism may be effectively slowed to a point where BOD removal is not sufficient to meet the effluent requirements.
As such, for an effective treatment, commercially formulated bacterial products need to be added to increase or restore the degradation process in an aerobic biological treatment system. The formulated bacteria will not only be added to increase the effective microbial population or to degrade the type of waste to be treated but also to introduce organisms which are better suited for conditions with high fluctuation e.g. temperature, pH, salinity, etc.
This process of addition or augmentation of an existing biomass is known as bioaugmentation.
Bioaugmentation
Bioaugmentation can be defined as the controlled application of specially selected natural microorganisms to enhance the performance of an operating biological wastewater treatment plant in order to improve final effluent quality or reduce operating costs.
In the aeration basin of a typical industrial wastewater treatment plant a biomass develops based on numerous strains of degradative and floc forming bacteria. This diversity of bacteria is necessary because different strains of bacteria are more effective in degrading different organic compounds. The biomass becomes adapted to the influent and will provide the required results provided a steady state of operation can be maintained. This is virtually impossible in an industrial plant where the influent characteristics can change drastically on a daily, or even hourly, basis.
Over time the desirable characteristics of the plant biomass may be reduced due to shocks and undesirable characteristics become more dominant. The use of bioaugmentation can boost the desirable population and reduce the undesirable population. Due to influent fluctuations and system upsets a maintenance dose is required to sustain the desired biomass population.
The purpose of bioaugmentation is to provide a controlled way of shifting the microbial population to one which is more effective in terms of degradation and settlement of the floc. This is achieved by enhancing the positive characteristics of the biomass and suppressing the more negative characteristics. It does not involve the total replacement of the existing biomass.
Successful bioaugmentation involves much more than product addition. It also involves a detailed survey of the plant and careful analysis of historical data to determine the cause of the problem and outline a remediation strategy. It also involves careful management of the system to ensure conditions are optimized for the added microbes and the biomass as a whole. For this reason simply dosing microbial products into the influent can not be considered to be bioaugmentation.
Some of the typical problems encountered in different industries give an indication of the role bioaugmentation can play in wastewater treatment.
2.0 Common Problems In Industrial Wastewater
i. Pulp And Paper
High BOD
Spills
Soap/Surfactant Loading
Increased Hydraulic Loading
Settling Problems
High/Low Temperatures
High Sulfide Problems
ii. Refinery
High TOC/COD/BOD
High Ammonia/ Loss of Nitrification
High/Low Temperatures
Start ups/Turnarounds
Toxic Overloads
Changes in Waste Streams
Increased Production
Oil & Grease
iii. Chemical Production
High COD/TOC
Amine Problems/Nitrification
Chlorinated Hydrocarbon Loading
High/Low Temperatures
Solvent/Surfactant Problems
Settling Problems
iv. Municipal
High BOD
High Oil & Grease
Foaming
Methane/H2S Recovery
Increased HRT
v. Dairy & Confectionary
High BOD & COD
High Oil & Grease
Odor problems
Denitrification
Foaming
Shock loading in Aeration Tank
vi. Others
Surfactant/Detergents
Odour Problems
FOG/Proteinaceous Waste
Cyanates
Diesel/Gasoline
3.0. Conclusion
Application of bacterial formulations to the treatment plant - the results achievable are as follows:-
Improving final effluent parameters (BOD, COD, and TSS).
Enhancing oil & grease degradation
Improving nitrification (Ammonia reduction).
Reducing toxicity.
Treating and preventing filamentous growth (bulking sludge).
Improving settling in the clarifier or sedimentation basin.
Reducing operational cost per M3 of water treated.
Stabilising the Food : Microorganisms ratio.
Maintaining effective & productive Biomass balance in Aeration Tank. Once stabilized, the Biomass will continue metabolising as long as the crucial parameters are controlled within the optimum level or standards e.g. pH, DO, temperature, F:M ratio, SVI, etc.
Speed-up WWTP recovery after plant upset due to shock-load, unwanted spillage, etc. Taking Biomass from other plants can be troublesome since it is virtually impossible to find a biomass which will be acclimated to the type of effluent which it will encounter. Also problems with the biomass will become more dominant in a new plant.
All species of bacteria formulated have been certified as Class I according to EU and WHO guidelines. The products are natural isolates and free from any pathogenic microorganisms and safe for humans, animals and plants.
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