Storage of biodegradable polymers by an enriched microbial community in a sequencing batch reactor operated at high organic load rate

The production of polyhydroxyalkanoates (PHAs) from organic acids by mixed bacterial cultures using a process based on aerobic enrichment of activated sludge, that selects for mixed microbial cultures able to store PHAs at high rates and yields, is described. Enrichment resulted from the selective pressure established by periodic feeding the carbon source in a sequencing batch reactor (SBR); a mixture of acetic, lactic and propionic acids was fed at high frequency (2 hourly), high dilution rate (1 d⁻¹), and at high organic load rate (12.75 g chemical oxygen demand (COD) L⁻¹ d⁻¹). The performance of the SBR was assessed by microbial biomass and PHA production as well as the composition and polymer content of the biomass. A final batch stage was used to increase the polymer concentration of the excess sludge produced in the SBR and in which the behaviour of the biomass was investigated by determining PHA production rates and yields. The microbial biomass selected in the SBR produced PHAs at high rate [278 mg PHAs (as COD) g biomass (as COD)⁻¹ h⁻¹, with a yield of 0.39 mg PHAs (as COD) mg removed substrates (as COD)⁻¹], reaching a polymer content higher than 50% (on a COD basis). The stored polymer was the copolymer poly(3‐hydroxybutyrate/3‐hydroxyvalerate) [P(HB/HV)], with an HV fraction of 18% mol mol⁻¹. The microbial community selected in the SBR was analysed by DGGE (denaturing gradient gel electrophoresis). The operating conditions of the SBR were shown to select for a restricted microbial population which appeared quite different in terms of composition with respect to the initial microbial cenosis in the activated sludge used as inoculum. On the basis of the sequencing of the major bands in the DGGE profiles, four main genera were identified: a Methylobacteriaceae bacterium, Flavobacterium sp, Candidatus Meganema perideroedes, and Thauera sp. The effects of nitrogen depletion (ie absence of growth) and pH variation were also investigated in the batch stage and compared with the SBR operative mode. Absence of growth did not stimulate higher PHA production, so indicating that the periodic feed regime fully exploited the storage potential of the enriched culture. Polymer production rates remained high between pH 6.5 and 9.5, whereas the HV content in the stored polymer strongly increased as the pH value increased. This study shows that polymer composition in the final batch stage can readily be controlled independently from the feed composition in the SBR. Copyright © 2005 Society of Chemical Industry     

Start up of biological sequencing batch reactor (SBR) and short‐term biomass acclimation for polyhydroxyalkanoates production

BACKGROUND: The adaptation/selection of mixed microbial cultures under feast/famine conditions is an essential step for polyhydroxyalkanoates (PHA) production. This study investigated the short‐term adaptation of a mixed microbial culture (activated sludge) during the start up of a sequencing batch reactor (SBR). RESULTS: Four different SBR runs were performed starting from different inocula and operated at the same organic load rate (8.5 gCOD L^?1 d^?1) and hydraulic retention time (1 day). At 3–7 days from SBR start up, the selected biomass was able to store PHA at comparable rate and yield with those obtained after long‐term acclimation. Independently from the time passed, a short feast phase was the key parameter to obtain PHA storage at high rate and yield in the following accumulation stage (244 mgCOD g^?1CODnonPolym h^?1 for specific storage rate and 48% COD COD^?1 as PHA content in the biomass). The DGGE profiles showed that the good storage performance and the structure of the microbial community were not fully correlated. CONCLUSIONS: The results suggest a new strategy for operating the PHA accumulation stage directly in the SBR, after very short biomass adaptation, instead of using two separate reactors for biomass enrichment and PHA accumulation, respectively. © 2012 Society of Chemical Industry     

High power generation with simultaneous COD removal using a circulating column microbial fuel cell

BACKGROUND: A circulating column microbial fuel cell (MFC) with Cu anode and Au? Cu air cathode was used for power generation and chemical oxygen demand (COD) removal from synthetic wastewater. The column was operated in repeated‐fed batch mode using acclimated anaerobic sludge. The contents of the column MFC were circulated while the feed wastewater was fed to the reactor in fed‐batch mode. Effects of feed COD concentration and COD loading rate on voltage difference, power density and percentage COD removal were investigated. RESULTS: The highest voltage difference (650 mV), power density (40 W m^?2) were obtained with a feed COD of 6400 mg L^?1, yielding 45% COD removal with a COD loading rate of nearly 90 mg h^?1. Low COD loadings (<90 mg h^?1) caused substrate limitations, and high loadings (>90 mg h^?1) resulted in inhibition of COD removal and power generation. The highest percentage COD removal (50%) was obtained with feed COD content of 10.35 g L^?1 or a COD loading rate of 145 mg h^?1. CONCLUSION: The power densities obtained with the circulating column MFC were considerably higher than those reported in the literature due to elimination of mass transfer limitations by the high circulation rates, proximity of electrodes and small anode surface area used in this study. Further improvements may be possible with optimization of the operating parameters. Copyright © 2009 Society of Chemical Industry     

单级SBR厌氧/好氧/缺氧处理中期垃圾渗滤液深度脱氮

为了考察单级SBR处理实际中期垃圾渗滤液深度脱氮的可行性,采用单级SBR在“厌氧/好氧/缺氧”(AOA)运行方式下处理实际中期垃圾渗滤液。试验发现,厌氧/好氧/缺氧交替运行下驯化的微生物能在厌氧段消耗胞内糖原,并将水中部分溶解性有机物以聚羟基脂肪酸酯(PHAs)形式储存;在好氧段微生物消耗胞内PHAs,转化为胞内糖原,氨氧化的同时也伴随着同步硝化反硝化脱氮;好氧段氨氧化结束后贮存的碳源(PHAs和糖原)能为后置缺氧反硝化提供碳源。经长期试验研究,进水COD、NH₄⁺-N、TN浓度分别为6430～9372 mg·L^-1、1025.6～1327 mg·L^-1、1345.7～1853.9 mg·L^-1,出水COD、NH₄⁺-N、TN浓度能达到525～943 mg·L^-1、1.2～4.2 mg·L^-1、18.9～38.9 mg·L^-1。在未投加外碳源的情况下,SBR法AOA运行方式下能够实现中期垃圾渗滤液的深度脱氮,出水TN<40 mg·L^-1。其中,好氧段(DO<1 mg·L^-1)通过同步硝化反硝化去除TN占总去除量的1/3左右;缺氧后置反硝化去除的TN占总去除量的2/3左右。     

Production of polyhydroxyalkanoates by Ralstonia eutropha from volatile fatty acids

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible thermoplastics that can be synthesized in various microorganisms. Volatile fatty acids (VFAs) are produced by anaerobic treatment of organic wastes that can be utilized as inexpensive substrates for PHA synthesis. In this study, several Ralstonia eutropha strains were grown on the mixture of VFAs (acetic, propionic, and butyric acid) as its carbon and energy source for growth and PHA synthesis. R. eutropha KCTC 2658 accumulated PHAs up to 50% of dry cell weight from total 5 g/L of mixed VFAs (acetic acid: propionic acid: butyric acid=1: 2: 2). In batch culture of R. eutropha KCTC2658 in a 5 L fermentor, a homopolymer of poly(3-hydroxybutyrate) [P(3HB)] was produced from 20 g/L glucose as a sole carbon source with dry cell weight of 8.4 g/L and PHA content of 30%. In fed-batch culture, two feeding strategies, pulse or pH-stat, were applied to add VFAs to the fermentor. When VFAs were fed using pH-stat feeding strategy after 40 h, a copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] was produced with dry cell weight of 8.1 g/L, PHA content of 50%, and 3HV fraction of 20 mol%.     

Synthesis of hybrid magnetic molecularly imprinted polymers for the selective adsorption of volatile fatty acids from anaerobic effluents

A novel magnetic, structured (with ordered pores) and hybrid imprinted polymer (HMMIP) was synthesized to selectively adsorb volatile fatty acids (VFAs) from aqueous matrices. Usual characterization techniques showed that a mesoporous adsorbent was obtained with relatively low specific areas but that could selectively (imprinting factor of 1.64) remove isovaleric acid (used as template) from aqueous solutions and effluents containing VFAs with a good capacity (Q_e ~ 50 mg g^?1). From kinetic studies a pseudo‐nth‐order model showed the best fit to the experimental data and resulted in k _{n = 3} equal to 8 × 10^?4 g mg^?1 min^?1 whereas thermodynamic studies indicated that the adsorption of isovaleric acid onto HMMIP was endothermic and entropically driven. Reuse studies indicated that HMMIP loaded with VFA could be efficiently regenerated with acetone–water solution which led to an adsorption loss of ca 10% after three regeneration/reuse cycles and that the magnetic and specific adsorbent could be removed from complex matrices with an efficiency of ca 77%. Biochemical methane production assays showed that the addition of HMMIP to anaerobic batch reactors increased by four times the methane production due to the selective adsorption of VFAs. © 2020 Society of Chemical Industry     

Treatment of high‐fat‐containing dairy wastewater in a sequential UASBR system: influence of recycle

BACKGROUND: Raw cheese whey originating from white cheese production results in a strong and complex wastewater excessively rich in organic matter (chemical oxygen demand, COD = 28–65 g L^?1), fatty matter (14–24.5 g L^?1) and acidity (3.9–6.1 g L^?1). It was treated in a three‐stage configuration consisting of a pre‐acidification (PA) tank and sequential upflow anaerobic sludge bed reactors (UASBRs) at 2.8–7 g COD L^?1 day^?1 organic loading rates, during which the effects of effluent recycling at low rates and promoted SRB activity were investigated. Acidification, volatile fatty acids (VFA), COD and fatty matter removal and volatile solids were monitored throughout the system during the study. RESULTS: Recycling of the effluent promoted VFA and COD removal as well as pH stability in both stages of the UASBRs and the effluent where high alkalinity levels were recovered reducing alkali requirement to 0.05 g OH g^?1 COD_applied. Higher removal rates of 71–100 and 50–92% for VFA and COD were obtained by use of recycling. Fatty matter was removed at 63–89% throughout the study. Volatile solids build‐up was significant in the inlet zones of the UASBRs. CONCLUSIONS: The system produced efficient acidification in the PA tank, balanced pH levels and an effluent high in alkalinity and BOD/COD ratio. Efficient VFA removal and solids immobilization was obtained in both stages up to the highest loading rate. Recycling improved the system performance under high fatty matter loading conditions. A major advantage of the sequential system was that the second stage UASBR compensated for reduced performance in the first stage. Copyright © 2010 Society of Chemical Industry     

Simultaneous removal of carbon,nitrogen and phosphorus from wastewater by coupling two-step anaerobic digestion with a sequencing batch reactor

The objective of this study was to develop an integrated process for simultaneous removal of carbon, nitrogen and phosphorus from industrial wastewaters. The process consisted of a-two step anaerobic digestion reactor, for carbon removal, coupled with a sequencing batch reactor (SBR) for nutrient removal. In the proposed process, carbon is eliminated into biogas by anaerobic digestion: acidogenesis and methanogenesis. The volatile fatty acids (VFA) produced during the first step of anaerobic digestion can be used as electron donors for both dephosphatation and denitrification. In the third reactor (SBR) dephosphatation and nitrification are induced through the application of an anaerobic–aerobic cycle. This paper describes the first trials and experiments on the SBR and a period of 210 days during which the SBR was connected to the acidogenic and methanogenic reactors. It was shown that nitrification of ammonia took place in the SBR reactor, during the aerobic phase. Furthermore, denitrification and VFA production were achieved together in the acidogenic reactor, when the efflux of nitrates from the SBR reactor was added to the first reactor influx. The proposed process was fed with a synthetic industrial wastewater, the composition of which was: total organic carbon (TOC)=2200 mg dm⁻³, total Kjeldahl nitrogen (TKN)=86 mg dm⁻³, phosphorus under phosphate form (P-PO₄)=20 mg dm⁻³. In these conditions, removals of carbon, nitrogen and phosphorus were 98%, 78% and 95% respectively. The results show that the combination of the two-step anaerobic digestion reactor and an SBR reactor is effective for simultaneous carbon, nitrogen and phosphorus removal. Reactor arrangements enabled zones of bacterial populations to exist. Complete denitrification occurred in the acidogenic reactor and hence the anaerobic activity was not reduced or inhibited by the presence of nitrate, thus allowing high TOC removal. Stable phosphorus release and phosphorus uptake took place in the SBR after coupling of the three reactors. A fast-settling compact sludge was generated in the SBR with the operational conditions applied, thus giving good separation of supernatant fluid. The benefits from this process are the saving of (i) an external carbon source for denitrification and phosphorus removal, (ii) a reactor for the denitrification step. © 1998 Society of Chemical Industry     

The start‐up of anaerobic sequencing batch reactors at 20 °C and 25 °C for the treatment of slaughterhouse wastewater

The objective of this research was to evaluate the feasibility, the stability and the efficiency of a start‐up at 20 °C and 25 °C of anaerobic sequencing batch reactors (ASBRs) treating slaughterhouse wastewater. Influent chemical oxygen demand (COD) and suspended solids concentrations averaged 7500 and 1700 mg dm^?3, respectively. Reactor start‐up was completed in 168 and 136 days at 20 °C, and 25 °C, respectively. The start‐up process was stable at both temperatures, except for a short period at 20 °C, when effluent volatile fatty acid (VFA) concentrations increased from an average of 40 to 400 mg dm^?3. Effluent quality varied throughout start‐up, but in the last 25 days of the experiment, as the ASBRs were operated under organic loading rates of 2.25 ± 0.21 and 2.86 ± 0.24 kg m^?3 d^?1 at 20 °C and 25 °C, respectively, total COD was reduced by 90.3% ± 1.3%. Methanogenesis was not a limiting factor during start‐up. At 20 °C, the limiting factor was the acidification of the soluble organics and, to a smaller extent, the reduction of propionic, isobutyric and isovaleric acids into lower VFAs. At 25 °C, the limiting factor was the hydrolysis of particulate organics. To minimize biomass loss during the start‐up period, the organic loading rate should be increased only when 75 –80% of the COD fed has been transformed into methane within the design hydraulic retention time. © 2001 Society of Chemical Industry     

Effect of Low Temperatures on the Performance of an Anaerobic Baffled Reactor (ABR)

The effect of a decrease in operating temperature on the performance of two 10 dm³ anaerobic baffled reactors (ABR) was examined in terms of steady state chemical oxygen demand (COD) removal efficiency. To minimise variations, and have a totally biodegradable feed, a synthetic carbohydrate (sucrose)–protein (meat extract) substrate was used. The reactors were operated at 20 h hydraulic retention time (HRT), 4 g dm⁻³ COD, and 35°C as a base-line condition. Because of their different histories, the reactors responded differently to a decrease in operating temperature to 25°C. Reactor 1 remained stable at 97% COD removal, whereas Reactor 2 decreased to 93% removal, but rose to 97% after adding an effluent recycle of 0·25. At 15°C, the efficiency of Reactor 1 dropped to 75%, while the removal of Reactor 2 declined to 83%, and no improvement in efficiency occurred with an effluent recycle at 0·25. At 25°C, the decreased rate of catabolism of the slow-growing syntrophs and methanogens resulted in a shift of the volatile fatty acids (VFA) peak to the second compartment. However, the biomass present in the reactor prevented VFAs breaking through in the effluent. Nevertheless, at 15°C VFAs were present in the effluent, perhaps due to the lower rates of metabolism and an increase in the K_s for VFAs. Finally, at 15°C part of the increase in the effluent COD was due to the enhanced production of soluble microbial products (SMP), or a decrease in their metabolism, with these compounds constituting some 10% of the inlet COD. © 1997 SCI.     

Enhanced biodegradation of 2‐chloronitro‐benzene using a coupled zero‐valent iron column and sequencing batch reactor system

BACKGROUND: This study focused on the effectiveness of the zero‐valent iron (ZVI) pre‐treatment for enhancing the biodegradability of 2‐chloronitrobenzene (2‐ClNB), and further to evaluate the performance and mechanism of a coupled ZVI column–sequencing batch reactor (SBR) system treating 2‐ClNB contained wastewater. RESULTS: 2‐ClNB was readily transformed into 2‐chloroaniline (2‐ClAn) with the efficiency over 99.9% by ZVI column, and its biodegradability was significantly enhanced via ZVI pretreatment. The transformed effluent was subsequently fed into the SBR followed by 2‐ClAn loading of 3.4–117.2 g m^?3 d^?1 and COD loading around 1000 g m^?3 d^?1. A 2‐ClAn removal efficiency over 99.9% and COD removal efficiency of 82.0–98.1% were obtained. Moreover, 91.9 ± 0.1% TOC removal efficiency and 107.1 ± 6.0% chloride recovery efficiency during one cycle confirmed the complete biodegradation of 2‐ClAn in the coupled system. 16S rDNA PCR‐DGGE analysis suggested that ZVI pretreatment enhanced the diversity of the microbial community and promoted enrichment of the functional microorganisms degrading 2‐ClAn in the following SBR. CONCLUSION: ZVI pretreatment significantly enhanced the biodegradability of 2‐ClNB, and the coupled ZVI–SBR system demonstrated excellent performance when treating wastewater containing 2‐ClNB. Copyright © 2011 Society of Chemical Industry     

Biological nutrient removal with volatile fatty acids from food wastes in sequencing batch reactor

Volatile fatty acids (VFAs) derived from food waste were used as an alternative carbon source in biological nutrient removal. The pH Profiles were monitored during the nutrient removal in an Na-acetate fed sequencing batch reactor (SBR) (C source). Effluent N, P and SCOD concentrations of 0.5 and 0.1 mg/L were achieved with 5.5 hour of HRT (hydraulic retention time) when influent concentrations of NH₄⁺-N, PO₄³⁻ and SCOD were 42.5, 5.92 and 180 mg/L. Then the SBR was fed with four solutions of VFAs produced under different acidogenesis conditions of food wastes. VFAs-added SBR showed similar specific nitrification rates (3.0 to 3.9 mg-N/g MLSS · h) to that of acetate, but specific denitrification rates (3.2 to 4.2 mg NO₃⁻N/g MLSS·h) were slightly lower than with acetate of 4.67 mg NO₃⁻-N/g MLSS·h. VFAs-introduced SBR efficiently removed phosphorus except when the SBR was fed with a VFA-solution containing high amounts of valerate and caproate.     

The effect of organic loading rate on the anaerobic digestion of two‐phase olive mill solid residue derived from fruits with low ripening index

A study of the effect of organic loading rate on the performance of anaerobic digestion of two‐phase olive mill solid residue (OMSR) was carried out in a laboratory‐scale completely stirred tank reactor. The reactor was operated at an influent substrate concentration of 162 g chemical oxygen demand (COD) dm^?3. The organic loading rate (OLR) varied between 0.8 and 11.0 g COD dm^?3 d^?1. COD removal efficiency decreased from 97.0% to 82.6% when the OLR increased from 0.8 to 8.3 g COD dm^?3 d^?1. It was found that OLRs higher than 9.2 g COD dm^?3 d^?1 favoured process failure, decreasing pH, COD removal efficiency and methane production rates (Q_M). Empirical equations described the effect of OLR on the process stability and the effect of soluble organic matter concentration on the total volatile fatty acids (TVFA)/total alkalinity (TAlk) ratio (ρ). The results obtained demonstrated that rates of substrate uptake were correlated with concentration of biodegradable COD, through an equation of the Michaelis–Menten type. The kinetic equation obtained was used to simulate the anaerobic digestion process of this residue and to obtain the theoretical COD degradation rates in the reactor. The small deviations obtained (equal to or lower than 10%) between values calculated through the model and experimental values suggest that the proposed model predicts the behaviour of the reactor accurately. Copyright © 2007 Society of Chemical Industry     

Process kinetics of UASB reactors treating non‐inhibitory substrate

The degradation of a non‐inhibitory substrate (sucrose) in upflow anaerobic sludge bed (UASB) reactors with different superficial flow velocites (u_s) was performed to generate experimental data. Additionally, a kinetic model accounting for the mass fraction of methanogens (f) and granule size distribution in UASB reactors is also proposed. At the volumetric loadings of 2.65–21.16 g COD dm^?3 day^?1, both the COD removal efficiency and granule size of the UASB reactors increase with increasing u_s. The f values determined experimentally increase from 0.13–0.24 to 0.27–0.43 if the volumetric loading is increased from 2.65 to 5.29 g COD dm^?3 day^?1. With a further increase in volumetric loading, the f values decline because of the accumulation of volatile fatty acids (VFAs). The predicted residual concentrations of VFAs and COD are in fairly good agreement with the experimental data. From the calculated effectiveness‐factor values, the influence of mass transfer resistance of the substrate sucrose on the overall substrate removal rate should not be neglected. From parametric sensitivity analyses together with the simulated concentration profiles, methanogenesis is the rate‐limiting step. Copyright © 2003 Society of Chemical Industry     

Bioconversion of residual soybean oil into polyhydroxyalkanoates

The aim of this study is to evaluate the bioconversion of residual soybean oil (RSO) into polyhydroxyalkanoates (PHAs) by selecting microorganism and fermentation condition in order to increase PHAs production. PHAs production by Cupriavidus necator IPT 026 using glucose (PHA 1) and RSO (PHA 2) as substrate is 1.15 ± 0.21 and 2.84 ± 0.04 g L^?1, respectively. FTIR spectra of PHAs were similar to data reported in literature. PHAs presented low crystallinity (PHA 1: 42.69%; PHA 2: 46.44%), high thermal stability (PHA 1: 271.78 °C; PHA 2: 272.52 °C), and low M_W (PHA 1: 140.69 kDa; PHA 2: 254.54 kDa). PHAs produced by RSO are potential candidates for industrial applications, especially ones that demand higher temperatures. This is the first study on the production and characterization of PHAs obtained by C. necator IPT 026 in culture with RSO. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46255.     

Removal of oxytetracycline (OTC) in a synthetic pharmaceutical wastewater by sequential anaerobic multichamber bed reactor (AMCBR)/completely stirred tank reactor (CSTR) system: biodegradation and inhibition kinetics

BACKGROUND: The antibiotics in industrial and munipical wastewaters could not be removed effectively in conventional anaerobic and aerobic biological treatment plants. Few studies have been performed to investigate the biodegradation and inhibition kinetics of oxytetracycline (OTC) on methanogens and total volatile fatty acids (TVFA). RESULTS: A high rate anaerobic multichamber bed reactor (AMCBR) was effective in removing the molasses‐chemical oxygen demand (COD), and the OTC antibiotic with yields as high as 96% at an influent OTC loading rate of 133.33 gOTC m^?3 day^?1 at a hydraulic retention time (HRT) of 2.25 days. Increasing the OTC loading rates from 22.22 gOTC m^?3 day^?1 to 133.33 gOTC m^?3 day^?1 improved both hydrolysis and specific utilization of molasses‐COD. The inhibition constants of TVFA (K_I?TVFA?meth) and OTC (K_I?OTC?meth) on methanogens decreased at OTC loadings > 133.33 gOTC m^?3 day^?1. The direct effect of OTC loadings > 133.3 gOTC m^?3 day^?1 on acidogens and methanogens was evaluated using the Haldane inhibition kinetic. CONCLUSION: OTC antibiotic was effectively removed in a sequential AMCBR/completely stirred tank reactor (CSTR). The Haldane inhibition constant (K_ID) decreased significantly at high OTC loads indicating the increase in toxicity. Copyright © 2012 Society of Chemical Industry     

Performance evaluation of batch and unsteady state fed‐batch reactor operations for the production of a marine microbial surfactant

BACKGROUND: Biosurfactants are microbially derived surface‐active and amphipathic molecules produced by various microorganisms. These versatile biomolecules can find potential applications in food, cosmetics, petroleum recovery and biopharmaceutical industries. However, their commercial use is impeded by low yields and productivities in fermentation processes. Thus, an attempt was made to enhance product yield and process productivity by designing a fed‐batch mode reactor strategy. RESULTS: Biosurfactant (BS) production by a marine bacterium was performed in batch and fed‐batch modes of reactor operation in a 3.7 L fermenter. BS concentration of 4.61 ± 0.07 g L^?1 was achieved in batch mode after 22 h with minimum power input of 33.87 × 10³ W, resulting in maximum mixing efficiency. The volumetric oxygen flow rate (K_La) of the marine culture was about 0.08 s^?1. BS production was growth‐associated, as evident from fitting growth kinetics data into the Luedeking‐Piret model. An unsteady state fed batch (USFB) strategy was employed to enhance BS production. Glucose feeding was done at different flow rates ranging from 3.7 mL min^?1 (USFB‐I) to 10 mL min^?1 (USFB‐II). USFB‐I strategy resulted in a maximum biosurfactant yield of 6.2 g l^?1 with an increment of 35% of batch data. The kinetic parameters of USFB‐I were better than those from batch and USFB‐II. CONCLUSION: Comparative performance evaluation of batch and semi‐continuous reactor operations was accomplished. USFB‐I operation improved biosurfactant production by about 35% over batch mode. USFB‐I strategy was more kinetically favorable than batch and USFB‐II. © 2012 Society of Chemical Industry     

Biodegradability of slaughterhouse wastewater with high blood content under anaerobic and aerobic conditions

In this work, the biodegradability of wastewater from a slaughterhouse located in Ke?an, Turkey, was studied under aerobic and anaerobic conditions. A very high total COD content of 7230 mg dm^?3 was found, due to an inefficient blood recovery system. Low BOD₅/COD ratio, high organic nitrogen and soluble COD contents, were in accordance with a high blood content. A respirometry test for COD fractionation showed a very low readily biodegradable fraction (S_S) of 2%, a rapidly hydrolysable fraction (S_H) of 51%, a slowly hydrolysable fraction (X_S) of 33% and an inert fraction of 6%. Kinetic analysis revealed that hydrolysis rates were much slower than these of domestic sewage. The results underlined the need for an anaerobic stage prior to aerobic treatment. Tests with an anaerobic batch reactor indicated efficient COD degradation, up to around 80% removal. Further anaerobic degradation of the remaining COD was much slower and resulted in the build up of inert COD compounds generated as part of the metabolic activities in the anaerobic reactor. Accordingly, it is suggested that an appropriate combination of anaerobic and aerobic reactors would have to limit anaerobic degradation to around 80% of the tCOD and an effluent concentration above 1000 mg dm^?3, for the optimum operation of the following aerobic stage. © 2003 Society of Chemical Industry     

The effect of substrate on the composition of polyhydroxyalkanoates in enhanced biological phosphorus removal

This paper primarily evaluates the effect of external substrate type on the composition of polyhydroxyalkanoates in enhanced biological phosphorus removal (EBPR). Two sets of sequencing batch reactors (SBRs) are operated for this purpose, one with acetate and the other with propionate as the sole carbon source at different influent COD/phosphate ratios in the range 6.7–20 mgCOD mg^?1P. Results indicate that propionate is a more efficient substrate for EBPR, enabling total phosphate removal regardless of the change in COD/phosphate ratio. Total polyhydroxyalkanoates formation of 267–291 mgCOD L^?1 with a slight increase at higher influent phosphorus levels is observed for acetate experiments, and a slightly lower level of 250–280 mgCOD L^?1, with a similar trend for propionate experiments. The volatile fatty acid type and composition in the influent induces a significant difference in the polyhydroxyalkanoates composition of the two sets of activated sludge sustained in corresponding SBR systems. Propionate is mostly stored as 3‐hydroxy‐2‐methylvalerate and polyhydroxyvalerate, while acetate is stored as polyhydroxybutyrate. The P uptake rate in SBRs fed with propionate is considerably higher than that in the acetate reactors. Parallel batch experiments yield different results, especially for systems fed with acetate, indicating that the enzymatic system to metabolize propionate is not rapidly established, always yielding a dominant polyhydroxybutyrate fraction in the generated polyhydroxyalkanoates regardless of the level of propionate in the feed. Copyright © 2007 Society of Chemical Industry     

The Anaerobic Biodegradation of a Bagasse-Based Paper-Mill Waste in Fixed-Film Reactor

The high concentration of biodegradable constituents in waste-water derived from bagasse-based paper mills warrants the consideration of an anaerobic biotechnology process to recover biogas and reduce the pollution load. An anaerobic down-flow fixed-film bark reactor process was studied to treat waste-water generated from bagasse-based paper mills. At the anaerobic stage, 90–95% of the total chemical oxygen demand (COD) was removed at loading rates of 3–18 kg COD m%^?3 day%^?1 without supplying any nutrients or trace elements. A yield coefficient of 0.156 g cells (g COD) %^?1 was calculated at a high COD loading rate of 18 kg COD m%^?3 day%^?1. With the anaerobic treatment process it is estimated that 1 m³ of bagasse waste-water with a COD content of 13000 mg dm%^?3 can produce about 3.5 m³ of methane. Intermittent checks on the system alkalinity revealed that feed neutralization to maintain alkalinity would be necessary with sodium bicarbonate at approximately 2500 mg dm%^?3 for achieving steady-state high treatment efficiency.