Exploiting olive oil mill effluents as a renewable resource for production of biodegradable polymers through a combined anaerobic–aerobic process

BACKGROUND: The performance of a three‐stage process for polyhydroxyalkanoate (PHA) bioproduction from olive oil mill effluents (OME) has been investigated. In the first anaerobic stage OME were fermented in a packed bed biofilm reactor into volatile fatty acids (VFAs). This VFA‐rich effluent was fed to the second stage, operated in an aerobic sequencing batch reactor (SBR), to enrich mixed cultures able to store PHAs. Finally, the storage response of the selected consortia was exploited in the third aerobic stage, operated in batch conditions. RESULTS: The anaerobic stage increased the VFA percentage in the OME from 18% to ～32% of the overall chemical oxygen demand (COD). A biomass with high storage response was successfully enriched in the SBR fed with the fermented OME at an organic load rate of 8.5 gCOD L^?1 d^?1, with maximum storage rate and yield (146 mgCOD gCOD^?1 h^?1 and 0.36 COD COD^?1, respectively) very similar to those obtained with a synthetic VFA mixture. By means of denaturing gradient gel electrophoresis (DGGE) analysis, different bacterial strains were identified during the two SBR runs: Lampropedia hyalina and Candidatus Meganema perideroedes, with the synthetic feed or the fermented OMEs, respectively. In the third stage, operated at increasing loads, the maximum concentration of the PHA produced increased linearly with the substrate fed. Moreover, about half of the stored PHAs were produced from substrates other than VFAs, mostly alcohols. CONCLUSION: The results obtained indicate that the process is effective for simultaneous treatment of OME and their valorization as a renewable resource for PHA production. Copyright © 2009 Society of Chemical Industry     

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     

Enrichment of Anammox biomass from municipal activated sludge: experimental and modelling results

Anaerobic Ammonia Oxidising (Anammox) biomass was enriched from sludge collected at a municipal wastewater treatment plant, employing a Sequential Batch Reactor (SBR). After 60 days Anammox activity started to be detected, by consumption of stoichiometric amounts of NO₂^? and NH₄⁺ in the system. Fluorescence In Situ Hybridisation analysis confirmed the increase of Anammox bacteria concentration with time. A final concentration of enriched biomass of 3–3.5 gVSS dm^?3 was obtained, showing a Specific Anammox Activity of 0.18 gNH₄⁺‐N gVSS^?1 d^?1 The reactor was able to treat nitrogen loading rates of up to 1.4 kgN m^?3 d^?1, achieving a removal efficiency of 82 %. On the other hand, the start‐up and operation of the Anammox SBR reactor were consequentially modelled with the Activated Sludge Model nr 1, extended for Anammox. The simulations predicted quite well the experimental data in relation to the concentrations of nitrogenous compounds and can be used to estimate the evolution of Anammox and heterotrophic biomass in the reactor. These simulations reveal that heterotrophs still remain in the system after the start‐up of the reactor and can protect the Anammox microorganisms from a negative effect of the oxygen. Copyright © 2004 Society of Chemical Industry     

Modeling and simulation of the formation and utilization of microbial products in aerobic granular sludge

A mathematical model is established to simulate the formation of extracellular polymeric substances (EPS), soluble microbial products (SMP), and internal storage products (X_STO) in aerobic granular sludge. The sensitivity of these microbial products concentrations toward the key model parameters is analyzed. Independent experiments are conducted to find required parameter values and to test its predictive ability. The model is evaluated by using one‐cycle operating experimental results of a lab‐scale aerobic granule‐based sequencing batch reactor (SBR) and batch experimental results. Results show that the model is able to describe the microbial product dynamics in aerobic granules and provide further insights into a granule‐based SBR. The effect of the initial substrate and biomass concentrations on the formation of microbial products in aerobic granular sludge can therefore be analyzed by model simulation. A higher substrate concentration results in a greater concentration of EPS, SMP, and X_STO. An accumulation of biomass in the bioreactor leads to an increased production rate of EPS, SMP, and X_STO. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Start‐up and enrichment of a granular anammox SBR to treat high nitrogen load wastewaters

BACKGROUND: Landfill leachate is characterized by low biodegradable organic matter that presents difficulties for the complete biological nitrogen removal usually performed by conventional biological nitrification/denitrification processes. To achieve this, the anaerobic ammonium oxidation (anammox) process is a promising biological treatment. This paper presents an anammox start‐up and enrichment methodology for treating high nitrogen load wastewaters using sequencing batch reactor (SBR) technology. RESULTS: The methodology is based on the gradual increase of the nitrite‐to‐ammonium molar ratio in the influent (from 0.76 to 1.32 mole NO₂^?‐N mole^?1NH₄⁺‐N) and on the exponential increase of the nitrogen loading rate (NLR, from 0.01 to 1.60 kg N m^?3 d^?1). 60 days after start‐up, anammox organisms were identified by polymerase chain reaction (PCR) technique as Candidatus Brocadia anammoxidans. After one year of operation, NLR had reached a value of 1.60 kg N m^?3 d^?1 with a nitrogen (ammonium plus nitrite) removal efficiency of 99.7%. The anammox biomass activity was verified by nitrogen mass balances with 1.32 ± 0.05 mole of nitrite removed per mole of ammonium removed and 0.23 ± 0.05 mole of nitrate produced per mole of ammonium removed. Also, enrichment of anammox bacteria was quantified by fluorescence in situ hybridization (FISH) analysis as 85.0 ± 1.8%. CONCLUSIONS: This paper provides a methodology for the enrichment of the anammox biomass in a SBR to treat high nitrogen loaded wastewaters. Copyright © 2007 Society of Chemical Industry     

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     

SRT对富集高聚PHA能力嗜盐MMC的影响

调控菌群富集过程的工艺参数,富集具有高PHA积累能力的混合菌(MMC)是发酵生产PHA的第一步也是最重要的一步。采用批式培养条件,集中研究了污泥停留时间(SRT)对PHA积累菌群的富集作用。研究结果表明SRT影响富集MMC的底物降解速率(q_S),微生物积累PHA的速率(q_P)和PHA积累能力。长SRT(SRT4d)导致了较低的q_S,q_P和PHA细胞含量;过短的SRT(SRT1d)则降低了MMC的PHA转化率(Y_PHA/S)和PHA积累能力,刺激了非PHA积累菌群的快速增殖。研究确定的最佳SRT为2d,在此条件下富集的MMC最大PHA积累量可达细胞干重的56%。研究证明了SRT在选择嗜盐MMC中的重要作用,为快速富集PHA积累能力MMC奠定基础。     

Improvement of the settling properties of Anammox sludge in an SBR

Biological systems for the treatment of wastewater have to provide optimum sludge retention to achieve high removal efficiencies. In the case of slow‐growing micro‐organisms, such as anaerobic ammonia‐oxidizing (Anammox) bacteria, episodes of flotation involving biomass wash‐out are especially critical. In this study a strategy based on the introduction of a mix period in the operational cycle of the Anammox Sequencing Batch Reactor (SBR) was tested for its effects on biomass retention and nitrite removal. Using this new cycle distribution the biomass retention inside the reactor improved as the solids concentration in the effluent of the SBR decreased from 20–45 to 5–10 mg VSS dm^?3 and the biomass concentration inside the reactor increased from 1.30 to 2.53 g VSS dm^?3 in a period of 25 days. A decrease of the sludge volume index (SVI) from 108 to 60 cm³ g VSS^?1 was also observed. Complete depletion of nitrite was achieved in the reactor only with the new cycle distribution treating nitrogen loading rates (g N‐NO₂^? + g N‐NH₄⁺ dm^?3 d^?1) up to 0.60 g N dm^?3 d^?1. Copyright © 2004 Society of Chemical Industry     

Partial nitrification of sludge reject water using suspended and granular biomass

BACKGROUND: Partial nitrification–Anammox is a combined promising advanced biological process for the removal of nitrogen from wastewater, which allows important savings in energy consumption, sludge production, and organic carbon. Granular biomass appears to be an interesting alternative to conventional activated sludge, mainly because of its better settling properties. This study deals with the experimental results of a comparison between a conventional and a granular sequencing batch reactor (SBR) for the partial nitrification of reject water. RESULTS: After some days of operation, 30 days in the conventional SBR (system A) and 100 days in the granular SBR (system B), partial nitrification was achieved. Granular sludge showed much better settling properties than suspended biomass, with values of sludge volumetric index (SVI₁₀) of 130 mL g^?1 in system A and 38 mL g^?1 in system B. Consequently, the solids concentration within the granular reactor was three times higher than for the conventional system while the concentration of solids in the effluent was 10 times higher in the conventional SBR. Morphology, microstructure and microbial populations in both systems were also studied. CONCLUSION: A partial nitrification process was successfully achieved in both systems, obtaining an effluent with a NO₂^?‐N/NH₄⁺‐N ratio near 1, suitable for a following Anammox process. Granular biomass, mostly formed by round particles, showed better settling properties, leading to better sludge–effluent separation as well as higher biomass retention in the reactor. The granulation process does not affect bacterial populations, since they were the same in both systems. Copyright © 2011 Society of Chemical Industry     

Citric acid,biomass and cellular lipid production by Yarrowia lipolytica strains cultivated on olive mill wastewater‐based media

BACKGROUND: Olive mill wastewaters (OMWs) are an important residue and several physico‐chemical and/or biotechnological methods have been proposed for their treatment. RESULTS: The ability of three Yarrowia lipolytica strains to grow on and convert glucose‐enriched OMWs into added‐value compounds in carbon‐ and nitrogen‐limited shake‐flask cultures was assessed. Remarkable decolorization (up to 63%) and non‐negligible removal of phenolic compounds (up to 34%, w/w) occurred. In nitrogen‐limited cultures, the accumulation of cellular lipids was favored by OMW addition into the medium. In contrast, although remarkable quantities of citric acid (Cit) were produced in control experiments (cultures without OMW addition), in which Cit up to 18.9 g L^?1 was produced with yield of Cit synthesized per sugar consumed ～0.73 g g^?1), adaptation of cultures to media supplemented with OMWs reduced the final Cit quantity and conversion yield values achieved. In OMW‐based media, the highest concentration of citric acid produced was 18.1 g L^?1, with conversion yield ～0.51 g g^?1. In carbon‐limited cultures, despite the presence of inhibitory compounds in the medium (e.g. phenols), biomass production was enhanced with the addition of OMWs. The highest biomass concentration achieved was 12.7 g L^?1, with biomass conversion yield per sugar consumed ～0.45 g g^?1. Fatty acid analysis of cellular lipid produced demonstrated that adaptation of all strains in OMW‐based media favored the synthesis of cellular lipids that contained increased concentrations of cellular oleic acid. CONCLUSIONS: The Y. lipolytica strains tested can be regarded as possible candidates for simultaneous OMWs remediation and production of added‐value compounds. Copyright © 2011 Society of Chemical Industry     

Batch treatment of liquid fraction of pig slurry by intermittent aeration: process simulation and microbial community analysis

BACKGROUND: Manure treatment in intensive livestock farming is required to reduce the risk of negative environmental impacts by nitrogen disposal. Biological removal through intermittent aeration in a single bioreactor is a suitable method for this purpose. The characteristic operation based on the alternation of oxic/anoxic phases confers these systems with certain particularities in terms of process modelling and of understanding the microbial interactions. RESULTS: The performance of a sequencing batch reactor (SBR) treating raw liquid fraction of pig slurry (LFPS) under loading rates of 0.13 g N L^?1 d^?1 was studied. Three different aeration strategies were applied: (1) constant airflow; (2) dissolved oxygen (DO) set‐point; and (3) DO‐based real‐time control. The comparatively low aeration intensity applied throughout the third strategy resulted in the process being performed mainly via nitrite, implying a reduction on the requirements of organic carbon and oxygen. However, a decrease in the nitrification rate was observed under those conditions. Experimental results were satisfactorily simulated by a mathematical model focused on organic carbon and nitrogen removal. Microbial community structure analysis through denaturing gradient gel electrophoretic profiling of 16S rDNA genes showed that the aeration exerted a strong influence on the dominant microbial populations. The presence of the ammonia‐oxidizing species Nitrosomonas europaea, and of denitrifying bacteria related to Thauera sp. and Ralstonia sp., was detected in the strategy at low DO. CONCLUSION: Dependence of model statement and parameter values on the bioreactor operational patterns and piggery wastewater composition was evidenced. Oxygen limitation was responsible for a significant microbial shift in SBR treating LFPS. Copyright © 2009 Society of Chemical Industry     

Continuous production of poly‐β‐hydroxybutyrate by high‐cell‐density cultivation of Wautersia eutropha

BACKGROUND: Poly‐β‐hydroxybutyrate (PHB) accumulation is triggered by limitation of a nutrient other than carbon. The production cost of PHB is very high. In order to reduce this cost, continuous cultivation for the accumulation of PHB was investigated. The culture was first allowed to grow under fed‐batch conditions to yield a significant increase in biomass and PHB accumulation. Thereafter this high‐cell‐density biomass containing PHB was allowed to grow and maintained under conditions of continuous cultivation so that the overall process could be simplified and economised. RESULTS: For continuous cultivation a medium containing 90 g L^?1 fructose and 2.5 g L^?1 nitrogen (as urea) was fed continuously at a dilution rate of 0.1 h^?1. A steady state biomass of 27.7 g L^?1 with a PHB concentration of 5.5 g L^?1 was established in the bioreactor. This resulted in a continuous PHB productivity of 0.55 g L^?1 h^?1. CONCLUSION: The experiments have resulted in the development of a novel production technology involving the integration of batch, fed‐batch and continuous processes. At the same time the production of PHB under continuous cultivation increases the overall industrial importance of the system. Copyright © 2008 Society of Chemical Industry     

Removal of monochlorobenzene from air in a trickling biofilter at high loading rates

BACKGROUND: In this study, the biofiltration of air streams laden with monochlorobenzene (MCB) vapours was investigated using a trickling biofilter operated co‐currently. The device was filled with ceramic material and inoculated with an acclimated microbial culture. A neutralization process was carried out in a separate unit using crushed oyster shells. Long‐term biofilter performance was evaluated over a 10‐month period of continuous experiments under different influent pollutant concentrations from 0.10 to 1.75 g m^?3, sequentially stepped up through three different apparent air residence times of 60, 30, and 15 s. RESULTS: Pollutant removal was shown to be complete at influent concentrations up to 1.25, 0.75 and 0.20 g m^?3, and apparent air residence times of 60, 30, and 15 s, respectively. The maximum elimination capacity was found to be 95.0 g m_PM^?3 h^?1 for an influent concentration of 1.0 g m^?3 and an apparent air residence time of 30 s, corresponding to a loading rate of 120.0 g m_PM^?3 h^?1. Monochlorobenzene and biomass concentration profiles along the biofilter evidenced the dependence of microbial concentration distribution on the pollutant loading rate and the existence of a linear relationship between biomass concentration and specific pollutant removal rate, regardless of the operating conditions applied. A macrokinetic analysis shows that the MCB removal rate is zeroth order for low values of MCB concentration. A critical value of MCB concentration exists at all superficial air velocity at which the biomass growth is inhibited. A simple kinetic model is developed which is able to describe the inhibition behaviour under any operating conditions. CONCLUSION: The experimental results indicated that the system was effective and stable under various working conditions and over a long operating period, provided that the loading conditions corresponding to substrate inhibition of microbial growth are not exceeded. Copyright © 2012 Society of Chemical Industry     

The photosynthetic efficiency of Chlorella biomass growth with reference to solar energy utilisation

The photosynthetic efficiency (PE) of a growing algal culture was determined from the growth yield (Y), that is, biomass produced/light absorbed and the calorific value of the biomass (k); PE = kY. To obtain the maximum photosynthetic efficiency the algae were grown in light-limited chemostat cultures in urea-mineral salts media plus CO₂ and steady-states were obtained at different specific growth rates. With a given light input the biomass output rate was independent of the specific growth rate up to at least 70% of the maximum specific growth rate. The photosynthetic efficiency was independent of the incident light intensity over the range studied, 5.3–21.3 W m^?2. The light source had a spectral range of 400–700 nm and its mean wavelength was assumed to be 575 nm. The values of the maximum growth yields (YG , g dry weight kJ^?1) were 0.0153 for the Sorokin Chlorella strain 211/8k and 0.0206 for a newly selected mixed culture MA003 which consisted of an alga and three species of heterotrophic bacteria. The maintenance energy (m) of the mixed culture MA003 was in the range 0–0.32 kJ g^?1 dry weight h^?1 and the specific maintenance rate (mYG ) was in the range 0–0.0066 h^?1. In Chlorella strain 211/8k the maximum PE was 34.7% which corresponds to a quantum demand (n) of 6.6 per O₂ molecule evolved. In the mixed culture MA003 the maximum PE was 46.8% with 95% confidence limits, 42.7–51.5. This PE value corresponds to a quantum demand (n) of 4.8 per O₂ molecule evolved. These results call in question the current model of photosynthesis which predicts that the maximum PE with absorbed light of mean wavelength 575 nm should not exceed 29% and the minimum quantum demand, n = 8. From our results with culture MA003 it is deduced that the maximum practicable storage of total solar energy by algal biomass growth in vitro is 18%.     

Two Stages of N‐Deficient Cultivation Enhance the Lipid Content of Microalga Scenedesmus sp.

Scenedesmus sp. 14‐3 was identified as a suitable candidate for producing biodiesel. The present work studied the effects of nitrogen concentration on the biomass and lipid productivity of algae, the consumption of sodium nitrate, and the two‐stage N‐deficient cultivation that could enhance dramatically the accumulation of biomass and lipids of Scenedesmus sp. 14‐3. The two‐stage N‐deficient cultivation was described as follows: microalga Scenedesmus sp. 14‐3 was cultured under low light intensity (LL) for 10 days in an N‐deficient medium by 20 % inoculum concentration, and transferred to complete N‐depletion BG11 under high light intensity (HL) for 8 days. The highest lipid content of Scenedesmus sp. 14‐3 was 53.05 ± 0.08 % (10 % inoculum concentration) following the second stage of N‐deficient cultivation after 8 days. For the second stage of N‐deficient cultivation, the lipid content of Scenedesmus sp. 14‐3 was 49.85 ± 0.22 %, which was 1.8 times higher than that under low light intensity (LL) (46–48 μmol m^?2 s^?1 ) in 10 days. Meanwhile, the high algal biomass productivity was around 0.10 g L^?1 day^?1 after the first stage of N‐deficient cultivation (10 days) and the biomass productivity was around 0.037 g L^?1 day^?1 under the second stage of N‐deficient cultivation (8 days). The comparison under different culture conditions showed a significant effect of the two‐stage of N‐deficient cultivation on lipid accumulation of Scenedesmus sp. 14‐3. The two‐stage N‐deficient cultivation without centrifugation achieved a complete N‐depletion condition, but the two‐stage process required centrifugation which is unsuitable for commercialization and large‐scale utilization. In summary, two‐stage N‐deficient cultivation is a more suitable and effective culture method for commercial applications and dramatic accumulation of lipids than the two‐stage process.     

Effects of supplement additives on anaerobic biogas production

Anaerobic digestion (AD) converts biomass to biogas. However, its performance is often affected by the nutrient condition of AD substrate. In this study, a few substrate supplements were selected to promote the biogas production; MgO, FeCl₃, and cellulase were selected based on the result from elemental analyses of the biomass. The potential impact of the additives on AD process was evaluated by performing a series of biochemical methane potential (BMP) tests. BMP reactors with the substrate with one of the selected additives (i.e., MgO of 380 mg Mg L^?1, FeCl₃ of 88 mg Fe L^?1 or cellulase of 25 mg L^?1) exhibited higher microbial activity; 5–15% more biogas production was observed, compared to the blank. Microbial community analysis showed that different additives resulted in proliferation of different microbial species. Therefore, it was decided to add the mixture of the three additives to the biomass. Addition of the mixed additive resulted in 22% more gas production.     

High cell density fermentation via a metabolically engineered Escherichia coli for the enhanced production of succinic acid

BACKGROUND: Succinic acid is a valuable four‐carbon organic chemical with applications in many fields. It was found that cell mass was an important factor in succinic acid production by metabolically engineered Escherichia coli strains. In this work, high cell density fermentation was investigated for succinic acid production by a metabolically engineered strain SD121 with ldhA, pflB, ptsG mutation and heterogenous cyanobacterial ppc overexpression. RESULTS: Under two‐stage cultivation, the controlled DO feeding strategy during the aerobic growth phase facilitated biomass up to a dry cell weight of 19.6 g L^?1, and enhanced succinic acid production in the following anaerobic fermentation phase to a concentration of 116.2 g L^?1. A near theoretical maximum succinic acid yield of 1.73 mol mol^?1 glucose was achieved with an average productivity of 1.55 g L^?1 h^?1. CONCLUSION: The results indicated the potential advantage of high cell density fermentation for improvement of succinic acid production by E. coli. Copyright © 2010 Society of Chemical Industry     

Modeling Kinetics of Anaerobic Co-Digestion of Poultry Litter and Wheat Straw Mixed with Municipal Wastewater in a Continuously Mixed Digester with Biological Solid Recycle Using Batch Experimental Data

The half-saturation rate coefficient and maximum rate constant in the Monod model, yield coefficient defined as the ratio of microbial mass to substrate mass, and endogenous decay coefficient are important kinetic parameters for design of anaerobic digestion. These parameters are usually determined from a continuous stable operation of anaerobic digestion, which is more difficult and complex than batch operation in laboratory scale. In this study, a novel method has been developed to determine those parameters from data of batch experiments. To verify this method, kinetics of batch anaerobic co-digestion of poultry litter and wheat straw mixed with municipal wastewater at three total solid (TS) levels (2, 4, and 8% TS) and 50% volatile solid (VS) of wheat straw (VSWS) were investigated. The results showed that the maximum specific methane volume (209?mL (initial g?VS)^?1)) was reached at 4% TS of 50% VSWS. Using the developed method, the kinetic parameters of endogenous decay coefficient, yield coefficient, maximum rate constant, and half-saturation coefficient were determined to be between 0.57?×?10^?3 and 1.2?×?10^?3?d^?1, 0.00938 and 0.0644?g volatile suspended solid (VSS) (VS)^?1, 1.394 and 13,797?d^?1, and 1.6?×?10^?8 and 99,996?g. The kinetic parameters obtained were used to simulate kinetic behaviors of a continuous mixed digester with biological solid recycle. The simulated results showed that the dilution rate was very significant for methane volume produced, VS and VSS concentrations in digestion operation. The maximum methane volume could be predicted to be 3071 and 4152?mL for 2 and 4% TS, respectively.     

复合菌群利用模拟APG协同FNA预处理剩余污泥水解液合成PHA

为探究亚硝酸（FNA）预处理协同烷基糖苷（APG）处理剩余污泥水解液合成聚羟基烷酸酯（PHA）的可行性,本文启动接种两种不同污泥的序批式反应器（SBR）富集PHA产生菌,研究活性污泥复合菌群以模拟APG协同FNA预处理剩余污泥的水解液为底物的PHA合成效果;并采用批次合成实验,考察pH、C/N和C/P对PHA合成量的影响。结果表明：与接种污水厂二沉池污泥的反应器（SBR^#1）相比,接种以葡萄糖为底物驯化成熟的产PHA混合菌的反应器（SBR^#2）在30天时得到的PHA合成量较高;随着富集时间的推移,到117天时,接种污水厂二沉池污泥得到的PHA产生菌性能更优。PHA合成的最佳条件为：pH=8,C/P=100∶0.03,C/N=125∶1。在此条件下,PHA合成量最大,为57.34%。以实际FNA预处理协同APG处理剩余污泥水解液为底物时,PHA的累积合成量为24.43%。该研究结果可丰富污泥合成PHA技术方法,为污泥的处理和资源化利用提供技术支持。