Özlem Karahan

The effect of residual microbial products on the experimental assessment of the particulate inert COD in wastewaters

Abstract This study mainly investigated the conceptual and experimental aspects related to the assessment of the particulate inert COD in tannery, domestic and synthetic wastewaters. The assumption of a constant fEX coefficient defining the residual fraction of endogenous biomass was not justified. Experimental proof was provided for the effect of residual microbial products generation, both soluble and particulate, on the assessment of inert COD fractions of different wastewaters. The results enabled the description of a unified procedure for the experimental assessment of inert COD fractions of wastewaters, as well as residual microbial products.

Industrial wastewater treatment by activated sludge

Industrial pollution is still a major concern and despite its significance, sound and systematic pollution control efforts are very poorly documented. The character and treatability of industrial wastewaters is highly variable and specific for each industrial activity. Biological treatment with activated sludge is the appropriate technology for industrial wastewaters from several major industrial sectors. Industrial Wastewater Treatment by Activated Sludge deals with the activated sludge treatment of industrial wastewaters by considering conceptual frameworks, methodologies and case studies, in a stepwise manner. The issues related to activated sludge treatment, such as biodegradability based characterization, modeling, assessment of stoichiometric and kinetic parameters and design, as well as the issues of industrial pollution control, e.g. in-plant control, effect of pretreatment, etc. are combined in a way to provide a comprehensive and information-rich view to the reader. By doing so, the book supplies an up-to-date reference for industrial wastewater experts and both graduate and undergraduate students. Industrial Wastewater Treatment by Activated Sludge provides a roadmap, describing the methodologies for the treatment of industrial wastewaters from several major sectors, based on a solid theoretical background. Up to now although valuable separate efforts both on activated sludge and industrial wastewater treatment have been presented, an integrated approach that is crucial to practice has not been available. This gap is filled by this book.

Validity of Monod kinetics at different sludge ages - Peptone biodegradation under aerobic conditions

The study presented an evaluation of the effect of culture history (sludge age) on the growth kinetics of a mixed culture grown under aerobic conditions. It involved an experimental setup where a lab-scale sequencing batch reactor was operated at steady-state at two different sludge ages (theta(X)) of 2 and 10 days. The system sustained a mixed culture fed with a synthetic substrate mainly consisting of peptone. The initial concentration of substrate COD was selected around 500 mg COD/L. Polyhydroxyalkanoate (PHA) storage occurred to a limited extent, around 30 mg COD/L for theta(X)=10 days and 15 mg COD/L for theta(X)=2 days. Evaluation of the experimental data based on calibration of two different models provided consistent and reliable evidence for a variable Monod kinetics where the maximum specific growth rate, was assessed as 6.1/day for theta(X)=2 days and 4.1/day for theta(X)=10 days. A similar variability was also applicable for the hydrolysis and storage kinetics. The rate of storage was significantly lower than the levels reported in the literature, exhibiting the ability of the microorganisms to regulate their metabolic mechanisms for adjusting the rate of microbial growth and storage competing for the same substrate. This adjustment evidently resulted in case-specific, variable kinetics both for microbial growth and substrate storage.

Biodegradability and denitrification potential of settleable chemical oxygen demand in domestic wastewater.

The effect of settling on mass balance and biodegradation characteristics of domestic wastewater and on denitrification potential was studied primarily using model calibration and evaluation of oxygen uptake rate profiles. Raw domestic wastewater was settled for a period of 30 minutes and a period of 2 hours to assess the effect of primary settling on wastewater characterization and composition. Mass balances in the system were made to evaluate the effect of primary settling on major parameters. Primary settling of the selected raw wastewater for 2 hours resulted in the removal of 32% chemical oxygen demand (COD), 9% total Kjeldahl nitrogen, 9% total phosphorus, and 47% total suspended solids. Respirometric analysis identified COD removed by settling as a new COD fraction, namely settleable slowly biodegradable COD (X(ss)), characterized by a hydrolysis rate of 1.0 day(-1) and a hydrolysis half-saturation coefficient of 0.08. A model simulation to test the fate and availability of suspended (X(s)) and settleable (X(ss)) COD fractions as carbon sources for denitrification showed that both particulate COD components were effectively removed aerobically at sludge ages higher than 1.5 to 2.0 days. Under anoxic conditions, the biodegradation of both COD fractions was reduced, especially below an anoxic sludge retention time of 3.0 days. Consequently, modeling results revealed that the settleable COD removed by primary settling could represent up to approximately 40% of the total denitrification potential of the system, depending on the specific configuration selected for the nitrogen removal process. This way, the results showed the significant effect of primary settling on denitrification, indicating that the settleable COD fraction could contribute an additional carbon source in systems where the denitrification potential associated with the influent becomes rate-limiting for the denitrification efficiency.

The effect of mixing pharmaceutical and tannery wastewaters on the biodegradation characteristics of the effluents

This paper evaluated the effect of mixing the effluent of a pharmaceutical plant producing acetylsalicylic acid with tannery wastewater, on the biodegradation of the effluents. The evaluation involved the analysis of the oxygen uptake rate (OUR), profiles of each wastewater and the mixture by respirometry. Model calibration using the experimental OUR data identified major COD fractions and associated process kinetics for all samples analyzed. The tannery sample was a plain-settled effluent having a total COD of around 2200 mg/L with a readily biodegradable fraction of 15%. The same fraction was 57% in the pharmaceutical wastewater sample having a much stronger total COD content of 40,435 mg/L. Consequently, mixing of the pharmaceutical effluent with the tannery wastewater up to 38% of the total COD in the mixture increased the readily biodegradable COD fraction but had an inhibitory effect on the biodegradation kinetics. This effect was relatively lower on growth, but quite significant on the hydrolysis of the slowly biodegradable COD decreasing the maximum hydrolysis rate from 2.0 day(-1) to 1.2 day(-1). Model evaluation of the respirometric data, as performed in this study sets a workable protocol for the assessment of the compatibility of different wastewater mixtures for biological treatability.

Effect of high nitrate concentration on PHB storage in sequencing batch reactor under anoxic conditions.

The study investigated effect of high influent nitrate concentration on poly-beta-hydroxybutyrate, (PHB), storage in a sequencing batch reactor, (SBR), under anoxic conditions. Acetate was fed as pulse during anoxic phase, sustained with external nitrate feeding. SBR operation involved three runs at steady state with COD/N ratios of 3.84, 2.93 and 1.54 gCOD/gN, where external nitrate concentrations gradually increased from 50 mg N/l to 114 mg N/l and 226 mg N/l, in 1st, 2nd and 3rd runs, respectively. In 1st run, acetate was fully converted into PHB with the storage yield value of 0.57-0.59 gCOD/gCOD, calculated both in terms of PHB formation and NO(X) utilization, confirming storage was the sole substrate utilization mechanism. In the following runs, PHB formation was reduced and the storage yield based on PHB dropped down to 0.40 and 0.33 gCOD/gCOD with increasing influent nitrate concentrations, indicating that higher portions of acetate were diverted to simultaneous direct growth. The observations suggested that nitrite accumulation detected at low COD/N ratios was responsible for inhibition of PHB storage.

Modelling biodegradation of nonylphenol ethoxylate in acclimated and non-acclimated microbial cultures

The biodegradation and inhibition kinetics of a commercial nonylphenol ethoxylate formulation were modelled for an activated sludge system fed with a synthetic substrate and nonylphenol ethoxylate mixture. Kinetic and stoichiometric coefficients of the proposed activated sludge model were obtained by employing on-line respirometry. Experimental as well as model results confirmed that nonylphenol ethoxylate exhibited non-competitive inhibition on the hydrolysis process with a coefficient of 150mg/L on the basis of COD and negatively influenced biomass growth through a competitive inhibition mechanism with a coefficient of 500mg/L on the basis of COD, when the biomass was not acclimated. Upon acclimation of the activated sludge system, the inhibition concentration for non-competitive inhibition on hydrolysis was increased to 5000mg/L, practically showing no inhibition, and the coefficient of competitive inhibition increased to 450mg/L, corresponding to a significant decrease in the inhibitory effects of NPEO on growth.

Fate of 2,6-dihydroxybenzoic acid and its inhibitory impact on the biodegradation of peptone under aerobic conditions

This study investigated the fate of 2,6-dihydroxybenzoic acid in a mixed microbial culture acclimated to peptone under aerobic conditions. A laboratory-scale sequencing batch reactor receiving a pulse feeding of peptone at the start of each daily cycle was used for this purpose. Experimental evaluations interpreted changes induced by continuous benzoic acid additions on the oxygen uptake rate profiles associated with peptone biodegradation. At first exposure, 2,6-dihydroxybenzoic acid reduced the activity of the mixed culture and impaired peptone biodegradation. Around one-third of peptone removed could be utilized for microbial metabolism. With continuous feeding the mixture culture became acclimated and simultaneously removed peptone and 2,6-dihydroxybenzoic acid. After 30 days, oxygen uptake rate tests performed separately on peptone, 2,6-dihydroxybenzoic acid and the substrate mixture supported the existence of a dual biomass restructured with the selective growth of another group of microorganisms capable of utilizing 2,6-dihydroxybenzoic acid as an organic carbon source.

Inhibition effect of linear alkylbenzene sulphonates on the biodegradation mechanisms of activated sludge.

The study presents a conceptual approach for the identification of the inhibition mechanisms of biodegradable inhibitors. Synthetic sewage was selected as the model degradable substrate to simulate domestic wastewaters. LAS, known to be a biodegradable but inhibitory compound, was selected as a model substrate for the determination of the inhibition mechanisms. Biodegradation of synthetic sewage and LAS were monitored through oxygen uptake rate (OUR) tests conducted to observe the dynamic response of the system when fed with synthetic sewage and synthetic sewage-LAS mixtures. The approach uses respirometry to calibrate the kinetic and stoichiometric coefficients of the proposed biochemical model. Model simulation results confirmed that presence of LAS has inhibitory effects on the biodegradation mechanisms of synthetic sewage. LAS imposed non-competitive inhibition on the hydrolysis process with an inhibition coefficient of 500 mg COD/L and effected heterotrophic growth through a competitive inhibition mechanism with an inhibition coefficient of 150 mg COD/L.

EFFECT OF PEROZONATION ON BIODEGRADABILITY AND TOXICITY OF A PENICILLIN FORMULATION EFFLUENT

The pretreatment of synthetic penicillin formulation effluent containing Procain Penicillin G (PPG) with the O3/H2O2 process (applied ozone dose = 1440 mg h−1 treatment time = 60 minutes; pH 7; H2O2 = 10 mM) was investigated. The effect of chemical pretreatment was assessed on the basis of acute toxicity and biodegradability with activated sludge using water flea Daphnia magna toxicity and activated sludge inhibition tests. Biological treatability studies were performed with a mixture of untreated or pretreated PPG effluent (25% on volume basis) and synthetic domestic wastewater simulating readily biodegradable organic substrate to simulate the characteristics of domestic wastewater (75% on volume basis). Pretreatment of PPG effluent the O3/H2O2 process resulted in more than 70% chemical oxygen demand (COD) removal and a 50% decrease in the acute toxicity towards Daphnia magna. On the other hand, biodegradation of untreated PPG effluent needed prolonged acclimation periods to obtain a significant biological COD removal (= 80%). Pretreatment employing the O3/H2O2 process not only decreased the ultimate biodegradability of PPG effluent but also increased its inhibitory effects on activated sludge treatment speculatively due to the formation of less biodegradable oxidation by-products.