Process Control of Activated Sludge Treatment

General feed forward controllers, conforming to standard control modes, have been derived for an activated sludge process. The analysis indicated that the appropriate controllers are proportional control with measurement of substrate flow rate, and derivative control with measurement of inlet substrate concentration, and manipulation of the rate of return sludge by both controllers. The performance of these controllers was tested by computer simulation of five dynamic aerator models with and without sludge storage, and with two settling basin models. In all cases significant reduction of the maximum exit substrate concentration was achieved. Additional improvement resulted from the use of sludge storage. As the aerator model became more linear the control results also improved. The first dynamic results were obtained using a perfect steady state settler model, the remainder assumed that the settler dynamics could be represented by a variable time delay. The addition of the settler dynamics caused the control to degrade somewhat. Finally the generality of the two controllers was proved mathematically for the five biological kinetic models for substrate utilization and bacterial growth

Behaviour of viruses in activated sludge treatment.

The behaviour of f2 coliphage and poliovirus I in activated sludge treatment was studied under different operating conditions of flow through time, mixed liquor suspended solids, temperature and virus loading in a bench scale model plant whose performance was similar to that of a full scale treatment plant. The liquid and solids fractions of mixed liquor samples containing virus were assayed separately, with the solids fraction receiving ultrasonic treatment. The recovery of poliovirus from mixed liquor by this method was about 83%, while that of f2 coliphage was in the range of about 54-85%. The average removal of f2 coliphage across the model plant was about 84 %, and was not significantly altered by altering the flow through time, mixed liquor suspended solids and temperature in the plant. The removal was, however, decreased from about 96 % to about 70% with higher virus loads. The association of f2 with the mixed liquor solids showed an inverse relation with increased flow, a direct relation with increased mixed liquor solids, and apparently direct relation (with an optimum) with increased temperature and a clear direct relation with increased virus load. The removal of poliovirus across the plant over the range of conditions studied was generally high and reached up to about 99.7 %. The behaviour and removal of both viruses in the model plant correlated with the association of these viruses with the suspended solids. The degree of association, which appeared to depend upon the nature of each virus and was achieved by physical adsorption, was strikingly contrasting with about 18 and 85 % of f2 and poliovirus respectively detected on the solids. The striking differences between the behaviour of f2 coliphage and poliovirus I imposed interesting implications on the concept of indicator virus from the public health viewpoint

The nitrogen and phosphorus budget of Flanders: a tool for efficient waste management and nutrient recovery

The region of Flanders in Belgium is, due to its high population density, intensive industry and livestock production, a nutrient-rich region. This results in important anthropogenic emissions to the environment, but also a large potential for the recovery and reuse of nitrogen (N ) and phosphorus (P) from waste streams. In this study, a substance flow analysis study for N and P is presented, in which the anthropogenic fluxes, stocks and hot spots of these two nutrients are quantified throughout the Flemish economy and environment. The environmental impact of the different economic sectors is addressed through the determination of the N and P footprint. The importance of food production in the nutrient cycle is thereby demonstrated through the large contribution of agriculture to the nutrient footprint (49% of N and 36% of P). Further focus is placed on the nutrient use efficiencies across the different sectors of the food supply nexus to target key nutrient losses and inefficiencies. This leads to an overall fertilizer-to-consumer efficiency of 14% for N and P, with the main nutrient losses originating from livestock production and food processing. At the end of the production and consumption chain, important nutrient quantities are embedded in concentrated waste streams such as excess manure, food processing waste streams and activated sludge. This demonstrates the large potential for nutrient recovery as a tool to improve nutrient use efficiencies and reduce the dependency of inorganic fertilizers. Several nutrient recovery strategies, both physicochemical and microbial, were evaluated for their economic feasibility and their impact on the primary energy demand of the total food supply chain

Process Control of Activated Sludge Treatment, Phase II

Material balances on substrate and microorganisms were derived in conjunction with various mixing configurations thought to accurately describe the activated sludge process. These models include the completely mixed with bypass, plug flow, and plug flow with bypass. Two sets of kinetic mechanisms for substrate utilization and bacterial growth were employed. A feed forward controller was designed from linear approximations of the material balances derived in the completely mixed with bypass mixing model. Utilizing frequency response methods, the controller was found essentially identical to a completely mixed modeled controller developed in a prior investigation. Through computer simulation the controller\u27s effectiveness was tested. The controller maintained suitable effluent quality principally through proportional control on the influent flow rate. Additional proportional derivative control on influent substrate concentration produced further reductions in substrate levels; however, when employing realistic forcing functions,these reductions were minor. Comparison of mixing models was dependent upon the degree of substrate loading inflicted on the system. Bypassing had a detrimental effect on effluent quality and process control. Experimental studies were performed to find a representative kinetic and mixing model which reproduces the diurnal fluctuations of key activated sludge process parameters found at the Lexington Wastewater Treatment Plant. A suitable model was not found as experimental and theoretical results did not agree

Application of NASA-developed technology to the automatic control of municipal sewage treatment plants

A search was made of NASA developed technology and commercial technology for process control sensors and instrumentation which would be applicable to the operation of municipal sewage treatment plants. Several notable items were found from which process control concepts were formulated that incorporated these items into systems to automatically operate municipal sewage treatment plants. A preliminary design of the most promising concept was developed into a process control scheme for an activated sludge treatment plant. This design included process control mechanisms for maintaining constant food to sludge mass (F/M) ratio, and for such unit processes as primary sedimentation, sludge wastage, and underflow control from the final clarifier

Activated Sludge and Other Aerobic Suspended Culture Processes

© 2011 by the authors. A review of the literature published in 2008, 2009 and 2010 relating to activated sludge treatment of wastewater is presented. The review considers information on the topics of modeling and kinetics; process microbiology; nitrogen and phosphorus removal; treatment and effects of xenobiotics; oxygen transfer; and solids separation

Fate of metallic engineered nanomaterials in constructed wetlands : prospection and future research perspectives

Metallic engineered nanomaterials (ENMs) undergo various transformations in the environment which affect their fate, toxicity and bioavailability. Although constructed wetlands (CWs) are applied as treatment systems for waste streams potentially containing metallic ENMs, little is known about the fate and effects of ENMs in CWs. Hence, literature data from related fields such as activated sludge wastewater treatment and natural wetlands is used to predict the fate and effects of ENMs in CWs and to analyze the risk of nanomaterials being released from CWs into surface waters. The ENMs are likely to reach the CW (partly) transformed and the transformations will continue in the CW. The main transformation processes depend on the type of ENM and the ambient environmental conditions in the CW. In general, ENMs are expected to undergo sorption onto (suspended) organic matter and plant roots. Although the risk of ENMs being released at high concentrations from CWs is estimated low, caution is warranted because of the estimated rise in the production of these materials. As discharge of (transformed) ENMs from CWs during normal operation is predicted to be low, future research should rather focus on the effects of system malfunctions (e.g. short-circuiting). Efficient retention in the CW and increasing production volumes in the future entail increasing concentrations within the CW substrate and further research needs to address possible adverse effects caused

A critical review of the formation of mono- and dicarboxylated metabolic intermediates of alkylphenol polyethoxylates during wastewater treatment and their environmental significance

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2010 Taylor & Francis.Alkylphenoxyacetic acids, the metabolic biodegradation products of alkylphenol ethoxylates, are commonly found in wastewaters and sewage effluents. These persistent hydrophilic derivatives possess intrinsic estrogenic activity, which can mimic natural hormones. Their concentrations increase through the sewage treatment works as a result of biodegradation and biotransformation, and when discharged can disrupt endocrine function in fish. These acidic metabolites represent the dominant alkylphenolic compounds found in wastewater effluent and their presence is cause for concern as, potentially, through further biotransformation and biodegradation, they can act as sources of nonylphenol, which is toxic and estrogenic. The authors aim to assess the mechanisms of formation as well as elimination of alkylphenoxyacetic acids within conventional sewage treatment works with the emphasis on the activated sludge process. In addition, they evaluate the various factors influencing their degradation and formation in laboratory scale and full-scale systems. The environmental implications of these compounds are considered, as is the need for tertiary treatment processes for their removal

Fate of drugs during wastewater treatment

This is the post-print version of the final paper published in TrAC Trends in Analytical Chemistry. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2013 Elsevier B.V.Recent trends in the determination of pharmaceutical drugs in wastewaters focus on the development of rapid multi-residue methods. This review addresses recent analytical trends in drug determination in environmental matrices used to facilitate fate studies. Analytical requirements for further fate evaluation and tertiary process selection and optimization are also discussed.EPSRC, Northumbrian Water, Anglian Water, Severn Trent Water, Yorkshire Water, and United Utilities

The impact of process variables on the removal of PBDEs and NPEOs during simulated activated sludge treatment

Sewage effluent is known to be a major source of endocrine disrupting compounds entering the aquatic environment. More efficient wastewater treatment could reduce the environmental load but, in order to achieve this factors determining compound behaviour must be understood. The knowledge of compound fate is becoming increasingly important for risk assessments and to allow modifications to wastewater treatment works to facilitate treatment of these compounds. This work illustrates that the removal of some endocrine disrupting compounds from sewage treatment works effluent is dependent on parameters such as sludge age, influent concentrations, concentrations of co-metabolites and hydraulic retention time as well as physico-chemical compound properties. From this research it is apparent that the principle environmental risk of plybrominated diphenyl ether contamination after wastewater treatment is via sludge disposal routes. Treatment of wastewater containing nonylphenol polyethoxylate surfactants poses environmental risks via two routes, some nonylphenolic compounds may pass through into receiving waters and degradation products such as nonylphenol and short chain ethoxylate compounds will enter the environment via sludge disposal.