Estimation of denitrification potential with respiration based techniques

Denitrification with its prerequisite process nitrification, is a common practice to remove nitrogen from wastewater in activated sludge systems. Although the key factors detrimental to its performance are well recognised, not all links are implemented for optimal design and operation performance. The relation between detailed wastewater characterisation and denitrification potential (DP) is the most crucial example of information that should be better incorporated in design and optimisation procedures. The lumped parameters COD/N and BOD 5 /N (nowadays used in many design approaches) or empirical values of denitrification rates do not allow to predict precisely the denitrification potential due to a unique character of each activated sludge and wastewater. Advanced activated sludge models require the input of a significant number of parameters. Since the estimation of each parameter is difficult and time consuming, the choice of default values is an option but this can lead to erroneous predictions of reality. Far-simplified models, usually based on on-line measurement of process state variables, describe processes with the simplest kinetics what in turn restricts seriously their implementation.In this thesis a methodology is presented to estimate the DP in relation to wastewater and activated sludge characteristics. Two respiration techniques form the basis for two different approaches: the anoxic nitrate utilisation rate (NUR-) test and the aerobic oxygen utilisation rate (OUR-) test. The approach based on the NUR-test is a direct method for the assessment of the DP. The approach based on the OUR-test is an indirect method because a simplified model is necessary to transform oxygen utilisation rate to nitrate utilisation rate. The NUR-test, except of serving as a tool to estimate directly the DP, enables to acquire simplified denitrification kinetics and a relevant wastewater characterisation, leading consequently to a prediction of the denitrification capacity and nitrate effluent quality. Knowledge about actual activated sludge kinetics and wastewater (or other substrate) characteristics allows to establish relations between sludge loading rate and achievable denitrification rate.The OUR-test was the base to formulate the simplified nitrification-denitrification model, where estimated substrate conversion rates are used without biomass population dynamics. Moreover, the aerobic and anoxic organic biodegradable substrate conversions are modelled with the same relations with the only difference that for anoxic conditions appropriate reduction factors are incorporated in conversion kinetics to reflect a slower activity of activated sludge under denitrifying conditions. A novel methodology based on aerobic and anoxic respiration tests is proposed to estimate the reduction factors. The proposed model approach constitutes an alternative for both complex and far-simplified model approaches. It enables to predict the overall N-removal potential and N-effluent quality of a system, based on an actual detailed wastewater and activated sludge characterisation. Good results from dynamic and static testing of the model implicates its possible implementation in control strategies, like e.g. a feed-back control of the denitrification by a nitrate-rich recycle rate, anoxic volume or the addition of an external carbon source.The effect of a decrease in the biodegradable COD-fraction by pre-treatment (pre-precipitation) on the DP was examined. For an evaluation the developed respiration based methodologies were used to estimate the DP in relation to wastewater and activated sludge characteristics. Implemented optimisation procedures revealed that the original denitrification potential of the wastewater determines the process capacity and efficiency. Optimisation steps by the manipulation of technological parameters in the existing process configuration or control strategies may therefore improve process performance only to small extent.</p

Duurzame en robuuste sanitatie door decentralisatie

Kritiek op de huidige centralistische aanpak van sanitatie, transport, behandeling en hergebruik van huishoudelijk afval en afvalwater, en schets van een alternatief: DESAH (Decentrale Sanitatie en Hergebruik), waarbij wordt voldaan aan de criteria duurzaamheid, preventie en robuustheid. Scheiding van afvalstromen, eenvoudige zuiveringssystemen (anaeroob; biologisch), terugwinning van grondstoffen, en hergebruik in huishouden en landbouw spelen een belangrijke ro

Anaerobic treatment in decentralised and source-separation-based sanitation concepts

Anaerobic digestion of wastewater should be a core technology employed in decentralised sanitation systems especially when their objective is also resource conservation and reuse. The most efficient system involves separate collection and anaerobic digestion of the most concentrated domestic wastewater streams: black or brown water and solid fraction of kitchen waste. Separate collection using minimal amount of transport water besides saving this resource allows to apply a targeted treatment. A relatively small volume of digested effluent can be directly reused for fertilisation or processed when a high quality product is required. Clean nutrient production requires advanced multi-step treatment but the quality of products is risk-free. The issue of organic micro-pollutants and their accumulation in the environment is recently often addressed. Anaerobic treatment of total domestic wastewater stream can be applied as well. Treated in this way wastewater can be discharged or used for irrigation or fertilisation. The post-treatment will be usually required and its rate of complexity depends on the anaerobic effluent quality and local requirements for final effluent quality. A variety of technological solutions for treatment of domestic wastewater streams and reuse of resources is discussed in this pape

Enhanced primary treatment of concentrated black water and kitchen residues within DESAR concept using two types of anaerobic digesters

Anaerobic digestion of concentrated domestic wastewater streams - black or brown water, and solid fraction of kitchen waste is considered as a core technology in a source separation based sanitation concept (DESAR - decentralised sanitation and reuse). A simple anaerobic digester can be implemented for an enhanced primary treatment or, in some situations, as a main treatment. Two reactor configurations were extensively studied; accumulation system (AC) and UASB septic tank at 15, 20 and 25°C. Due to long retention times in an AC reactor, far stabilisation of treated medium can be accomplished with methanisation up to 60%. The AC systems are the most suitable to apply when the volume of waste to be treated is minimal and when a direct reuse of a treated medium in agriculture is possible. Digested effluent contains both liquid and solids. In a UASB septic tank, efficient separation of solids and liquid is accomplished. The total COD removal was above 80% at 25°C. The effluent contains COD and nutrients, mainly in a soluble form. The frequency of excess sludge removal is low and sludge is well stabilised due to a long accumulation tim

Effect of temperature on anaerobic treatment of black water in UASB-septic tank systems

The effect of northern European seasonal temperature changes and low temperature on the performance of upflow anaerobic sludge blanket (UASB)-septic tanks treating black water was studied. Three UASB-septic tanks were monitored with different operational parameters and at different temperatures. The results indicated the feasibility of the UASB-septic tank for (pre)treatment of black water at low temperatures with respect to removal of suspended solids and dissolved organic material. Inoculum sludge had little effect on CODss removal, though in the start-up phase some poorly adapted inoculum disintegrated and washed out, thus requiring consideration when designing the process. Removal of CODdis was at first negative, but improved as the sludge adapted to low temperature. The UASB-septic tank alone did not comply with Finnish or Dutch treatment requirements and should therefore be considered mainly as a pre-treatment method. However, measuring the requirements as mgCOD l-1 may not always be the best method, as the volume of the effluent discharged is also an important factor in the final amount of COD entering the receiving water bodie