Nazik Artan

Biological treatability of dairy wastewaters

Biological treatability of an integrated dairy plant wastewater containing a small fraction of whey-washwaters mixture has been experimentally investigated. Emphasis has been placed on the assessment of the initially inert fraction, S1 and soluble residual microbial products, Sp. Parallel batch experiments have been conducted to determine the kinetic and stoichiometric coefficients of the degradable COD. The results have shown that the wastewater tested had practically no initially inert fraction, but generated residual microbial products amounting to 6–7% of the initial degradable COD. The results obtained have been fed into a set of equations describing the steady state operation of an activated sludge system with sludge recycle and a relationship indicating the variation of the total effluent COD with the sludge age has been defined for the wastewater tested. It is noted that effluent COD cannot be biologically reduced below 85 mg l−1, regardless of the sludge age, due to generation of residual fractions.

Mechanism and Design of Sequencing Batch Reactors for Nutrient Removal

The sequencing batch reactor (SBR) is perhaps the most promising and viable of the proposed activated sludge modifications today for the removal of organic carbon and nutrients. In a relatively short period, it has become increasingly popular for the treatment of domestic and industrial wastewaters, as an effective biological treatment system due to its simplicity and flexibility of operation. Mechanism and Design of Sequencing Batch Reactors for Nutrient Removal has been prepared with the main objective to provide a unified design approach for SBR systems, primarily based on relevant process stoichiometry. Specific emphasis has been placed upon the fact that such a unified design approach is also by nature the determining factor for the selection of the most appropriate cyclic operation scheme, the sequence of necessary phases and filling patterns for the particular application. The proposed basis for design is developed and presented in a stepwise approach to cover both organic carbon and nutrient removal, domestic and industrial wastewaters, strong and specific wastes. The merits of model simulation as an integral complement of process design, along with performance evaluation of SBR models are also emphasized. This title belongs to Scientific and Technical Report Series ISBN: 9781843390824 (Print) ISBN: 9781780402604 (eBook)

Mechanism and design of intermittent aeration activated sludge process for nitrogen removal.

The paper provided a comprehensive evaluation of the mechanism and design of intermittent aeration activated sludge process for nitrogen removal. Based on the specific character of the process the total cycle time, (T C ), the aerated fraction, (AF), and the cycle time ratio, (CTR) were defined as major design parameters, aside from the sludge age of the system. Their impact on system performance was evaluated by means of process simulation. A rational design procedure was developed on the basis of basic stochiometry and mass balance related to the oxidation and removal of nitrogen under aerobic and anoxic conditions, which enabled selected of operation parameters of optimum performance. The simulation results indicated that the total nitrogen level could be reduced to a minimum level by appropriate manipulation of the aerated fraction and cycle time ratio. They also showed that the effluent total nitrogen could be lowered to around 4.0 mgN/L by adjusting the dissolved oxygen set–point to 0.5 mg/L, a level which promotes simultaneous nitrification and denitrification.

Population dynamics in a sequencing batch reactor fed with glucose and operated for enhanced biological phosphorus removal

The study investigated the effect of glucose feeding as the sole carbon source on population dynamics in a sequencing batch reactor (SBR) operated for enhanced biological phosphorus removal (EBPR). The lab-scale SBR operation was started with a biomass taken from a WWTP plant performing EBPR and continued around two months. It exhibited a sequence of periods with different performance and biomass characteristics. The first period indicated predominant EBPR activity, involving phosphorus release in the anaerobic phase with PHA production as expected. Lactate generated from glucose fermentation was presumably converted to PHA by PAOs as an essential part of the EBPR activity. In the second period a major shift occurred in the population dynamics favoring the preferential growth and the predominance of GAOs which have the advantage of utilizing glucose directly and eventually the EBPR activity was deteriorated. The significant feature of the third period was the proliferation of filamentous microorganisms.

Model evaluation of temperature dependency for carbon and nitrogen removal in a full-scale activated sludge plant treating leather-tanning wastewater

Organic carbon and nitrogen removal performance of a full-scale activated sludge plant treating pre-settled leather tanning wastewater was evaluated under dynamic process temperatures. Emphasis was placed upon observed nitrogen removal depicting a highly variable magnitude with changing process temperatures. As the plant was not specifically designed for this purpose, observed nitrogen removal could be largely attributed to simultaneous nitrification and denitrification presumably occurring at increased process temperatures (T > 25°C) and resulting low dissolved oxygen levels (DO < 0.5 mgO2/L). Model evaluation using long-term data revealed that the yearly performance of activated sludge reactor could be successfully calibrated by means of temperature dependent parameters associated with nitrification, hydrolysis, ammonification and endogenous decay parameters. In this context, the Arrhenius coefficients of (i) for the maximum autotrophic growth rate, A, (ii) maximum hydrolysis rate, khs and (iii) endogenous heterotrophic decay rate, bH were found to be 1.045, 1.070 and 1.035, respectively. The ammonification rate (ka) defining the degradation of soluble organic nitrogen could not be characterized however via an Arrhenius-type equation.

The fate of phosphate under anoxic conditions in biological nutrient removal activated sludge systems

The nitrogen removal potential of phosphate accumulating organisms under anoxic conditions has been evaluated using a laboratory scale sequencing batch reactor fed with synthetic wastewater and operated in a sequence of anaerobic, anoxic and aerobic periods. The phosphate uptake rate under anoxic conditions was lower than that under aerobic conditions. However, in the presence of an external substrate such as glucose and acetate, the fate of phosphate was dependent on the substrate type; phosphate release occurred in the presence of nitrate as long as acetate was present and glucose did not cause any phosphate release. The nitrate uptake rate was also much lower with glucose than acetate. The results implied that poly-hydroxyalkanoates could be oxidized by nitrate and phosphate uptake during the anoxic phase should be introduced into process modeling.

Effect of biomass concentration on the performance and modeling of nitrogen removal for membrane bioreactors

The study investigated the effect of biomass concentration on nitrogen removal in a membrane bioreactor by model evaluation of system performance. The steady state operation of a pilot membrane bioreactor fed with domestic sewage at a sludge age of 74 days and an average biomass concentration of 27,000 mg/L was monitored. The results were evaluated by calibration of a suspended growth model designed for this purpose and compared with those of an earlier experiment on the same system operated at a sludge age of 34 days, with a markedly lower biomass concentration. The membrane bioreactor always sustained a dissolved oxygen concentration of around 2 mgO2/L which could be explained by diffusion limitation of dissoved oxygen from the bulk liquid into the floc. Nitrogen removal was controlled and limited by nitrification which occurred only partially throughout the study. The oxidized nitrogen was always fully removed by means of simultaneous nitrification denitrification reducing the level of nitrate to a very low level so that the anoxic tank in front of the membrane bioreactor was totally useless in terms of nitrogen removal. Comparison of the results of the two experimental runs indicated that increasing the biomass concentration drastically changed the system behavior from denitrification limitation to nitrification limitation due to increased constraints on the mass transfer of dissolved oxygen. The selected model could be successfully calibrated for the model parameters by means of substantially higher oxygen half saturation constants for heterotrophs (KOH) and autotrophs (KOA) determined as 2.0 mgO2/L and 2.25 mgO2/L, respectively.

Modelling of long-term simultaneous nitrification and denitrification (SNDN) performance of a pilot scale membrane bioreactor.

Nutrient removal capability of the MBR process has attracted more attention than organics removal in the past few years. Apart from the conventional schemes for nitrogen removal in MBR process, simultaneous nitrification-denitrification (SNDN) requires the most attention for further research. In order to fully understand the fundemantals and mechanism of SNDN in MBRs, a pilot plant was set up. A mathematical model was adopted for investigation and calibration against the observed values. This paper reports a study focusing on evaluating major mechanisms that govern nitrogen removal from domestic wastewater in membrane bioreactors. Two items need to be emphasized in this evaluation: (i) an MBR is basically regarded as an activated sludge process-a suspended growth bioreactor with total biomass recycle and substantially higher biomass concentration; (ii) in this context an AS model, namely ASM1R modified for endogenous respiration, is used for dynamic modelling and calibration of experimental results. The impact of diffusion through biomass which obviously exerts a significant effect on system performance and denitrification is evaluated with success using the adopted model by means of switch functions that regulate nitrification-denitrification with respect to dissolved oxygen concentration in the bulk liquid.

Appropriate Design of Activated Sludge Systems for Nitrogen Removal from High Strength Wastewaters

Abstract The study is focused on defining a conceptual approach for the design of activated sludge systems treating strong wastewater for nitrogen removal. The effect of major factors such as COD/N ratio, denitrification potential, available nitrate, anoxic volume fraction, and recycle ratio is evaluated in terms of basic stoichiometry. An algorithm for appropriate design is developed for a continuous flow activated sludge and sequencing batch reactor, both operated in a pre-denitrification mode. The design approach is tested for two types of strong industrial wastewaters with different N contents and COD/N ratios and a typical domestic sewage for comparative evaluation.

Design of Sequencing Batch Reactors for Biological Nitrogen Removal from High Strength Wastewaters

Abstract This paper covers an evaluation of more than twenty full-scale industrial wastewater treatment plants employing sequencing batch reactor (SBR) process mainly for carbon removal and a pilot-scale SBR designed for carbon and nitrogen removal from tannery effluent. The study highlights the major features of the SBR technology and proposes a rational dimensioning approach for carbon and nitrogen removal SBRs treating high strength industrial wastewaters based on scientific information on process stoichiometry and modeling, also emphasizing practical constraints in design and operation.