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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.109, #1-3)

Introduction by Sergey V. Kalyuzhnyi; Peter Weiland (pp. 1-2).

Combining mixing regimes for optimized anaerobic wastewater treatment by Robbert Kleerebezem (pp. 3-13).

Operational practice of high-rate anaerobic bioreactors such as upflow anaerobic sludge bed (UASB) reactors is generally based on maximization of the biomass concentration and, in the case of more than one reactor compartment, operation in parallel. In this article, a modeling approach is used to postulate that the treatment performance of anaerobic bioreactors can be improved by simple operational measures. To achieve minimized effluent soluble substrate concentrations, operation of two reactors in series combined with active exchange of biomass between both reactors is suggested. In this way, substrate concentrations lower than the minimum achievable concentration in a completely mixed reactor can be achieved. It is furthermore suggested that maximized biomass concentrations (and solid retention times [SRTs]) do not necessarily lead to minimized effluent concentrations of organic material. At elevated SRTs, the soluble microbial products resulting from biomass turnover are shown to represent the main fraction of soluble organic material in the effluent of the reactor, limiting treatment efficiency.

Keywords: Anaerobic wastewater treatment; operation optimization; soluble microbial products; staged reactor concepts; upflow anaerobic sludge bed reactor

Modeling of anaerobic degradation of solid slaughterhouse waste by L. Y. Lokshina; V. A. Vavilin; E. Salminen; J. Rintala (pp. 15-32).

The anaerobic bioconversion of solid poultry slaughterhouse wastes was kinetically investigated. The modified version of simulation model was applied for description of experimental data in mesophilic laboratory digester and assays. Additionally, stages of formation and consumption of long chain fatty acids (LCFA) were included in the model. Batch data on volatile solids, ammonium, acetate, butyrate, propionate, LCFA concentrations, pH level, cumulative volume, and methane partial pressure were used for model calibration. As a reference, the model was used to describe digestion of solid sorted household waste. Simulation, results showed that an inhibition of polymer hydrolysis by volatile fatty acids and acetogenesis by NH₃ or LCFA could be responsible for the complex system dynamics during degradation of lipid-and protein-rich wastes.

Keywords: Ammonia; anaerobic digestion; inhibition; long-chain fatty acids; poultry slaughterhouse waste; model; sorted solid household waste

Extension of Enaerobic Digestion Model No. 1 with processes of sulfate reduction by Vyacheslav Fedorovich; Piet Lens; Sergey Kalyuzhnyi (pp. 33-45).

In the present work, the Anaerobic Digestion Model No. 1 (ADM1) for computer simulation of anaerobic processes was extended to the processes of sulfate reduction. The upgrade maintained the structure of ADM1 and included additional blocks describing sulfate-reducing processes (multiple reaction stoichiometry, microbial growth kinetics, conventional material balances for ideally mixed reactor, liquid-gas interactions, and licuid-phase equilibrium chemistry). The extended model was applied to describe a long-term experiment on sulfate reduction in a volatile fatty acid-fed upflow anaerobic sludge bed reactor and was generally able to predict the outcome of competition among acetogenic bacteria, methanogenic archaea, and sulfate-reducing bacteria for these substrates. The computer simulations also showed that when the upward liquid velocity in the reactor exceeds 1 m/d, the structure of the sludge becomes essential owing to bacterial detachment.

Keywords: Mathematical modeling; sulfate reduction; methanogenesis; competition; Anaerobic Digestion Model No. 1

Parameter identification of thermophilic anaerobic degradation of valerate by Xavier Flotats; Birgitte K. Ahring; Irini Angelidaki (pp. 47-62).

The considered mathematical model of the decomposition of valerate presents three unknown kinetic parameters, two unknown stoichiometric coefficients, and three unknown initial concentrations for biomass. Applying a structural identifiability study, we concluded that it is necessary to perform simultaneous batch experiments with differenitial conditions for estimating these parameters. Four simultaneous batch experiments were conducted at 55°C, characterized by four different initial acetate concentrations. Product inhibition of valerate degradation by acetate was considered. Practical identification was done optimizing the sum of the multiple determination coefficients for all measured state viariables and for all experiments simultaneously. The estimated values of kinetic parameters and stoichiometric coefficients were characterized by the parameter correlation matrix, the confidence interval, and the student's t-test at 9% significance level with positive results except for the saturation constant, for which more eperiments for improving its identifiability should be conducted. In this article, we discussekinetic parameter estimation methods.

Keywords: Anaerobic; mathematical modeling; identifiability; parameter estimation; optimization; valerate

Dynamic simulation of pH in anaerobic processes by Elena Campos; Xavier Flotats (pp. 63-76).

With the objective of contributing to the buildup of mathematical tools for anaerobic process simulation, an algorithm for the dynamic simulation of pH was developed. The dynamic simulation of the gaseous phase variables was also considered. The pH algorithm was validated for a watery system, obtaining good agreement between predicted and experimental data. The applied methodology provides a differential equation that allows the inclusion of pH as a state variable of the system that can be easily included in a general mathematical model of anaerobic digestion using matrix notation. This methodology also allows a noticeable decrease in computing time in simulations. A dynamic anaerobic digestion model of complex substrates taken from the literature was completed with the developed algorithms, and it was used to predict the response of an anaerobic reactor against overloading and against the presence of pH-dependent inhibitors with satisfactory results.

Keywords: Anaerobic digestion model; pH simulation; ammonia inhibition; physical-chemical processes; dynamical modeling

Sustainable treatment and reuse of diluted pig manure streams in Russia by Sergey Kalyuzhnyi; Vladimir Sklyar; Andrey Epov; Irina Arkhipchenko; Irina Barboulina; Olga Orlova; Alexander Kovalev; Alla Nozhevnikova; Abraham Klapwijk (pp. 77-94).

This article summarizes the results obtained during the laboratory and pilot development of integrated biologic and physicochemical treatment and reuse of diluted pig manure streams. The application of a straw filter was an effective means to separate the solid and liquid fractions of raw wastewater and resulted in the removal of a significant part of the dry matter, total nitrogen, and phosphorus (65, 27, and 32%, respectively). From the filtrate generated, 60–80% of the total chemical oxygen demand (COD) was removed in an upflow anaerobic sludge bed reactor operating at 15–30°C. Ammonia was efficiently eliminated (>99%) from the anaerobic effluents using Ural laumantite as an ion exchanger. However, the nitrogen-content of the zeolite was too low to consider this method of ammonia removal economically feasible. The phosphate precipitation block, consisting of stripper of CO₂ and fluidized-bed crystallizator, was able to decrease the concentration of soluble phosphate in the anaerobic effluents up to 7–15 mg of phosphate/L. The application of aerobic/anoxic biofilter as a sole polishing step was acceptable from an aesthetic point of view (the effluents were transparent and almost colorless and odorless) and elimination of biochemical oxygen demand (the resting COD was hardly biodegradable). However, the effluent nutrient concentrations (especially nitrogen) were far from the current standards for direct discharge of treated wastewater. We discuss the approaches for further improvement of effluent quality. Finally, we provide an outline of a full-scale system that partially implements the laboratory- and pilot-scale results obtained.

Keywords: Integrated system; nutrient removal; phosphate precipitation; pig manure wastewater; straw filter; upflow anaerobic sludge bed reactor; zeolite

Codigestion of manure and organic wastes in centralized biogas plants by I. Angelidaki; L. Ellegaard (pp. 95-105).

Centralized biogas plants in Denmark codigest mainly manure, together with other organic waste such as industrial organic waste, source sorted household waste, and sewage sludge. Today 22 large-scale centralized biogas plants are in operation in Denmark, and in 2001 they treated approx 1.2 million tons of manure as well as approx 300,000 of organic industrial waste. Besides the centralized biogas plants there are a large number of smaller farm scale plants. The long-term energy plan objective is a 10-fold increase of the 1998 level of biogas production by the year 2020. This will help to achieve a target of 12–14% of the national energy consumption being provided by renew able energy by the year 2005 and 33% by the year 2030. A major part of this increase is expected to come from new centralized biogas plants. The annual potential for biogas production from biomass resources available in Denmark is sstimated to be approx 30 Peta Joule (PJ). Manure comprises about 80% of this potential. Special emphasis has been paid to establishing good sanitation and pathogen reduction of the digested material, to avoid risk of spreading pathogens when applying the digested manure as fertilizer to agricultural soils.

Keywords: Anaerobic; centralized biogas plants; codigestion; thermophilic

Reducing waste contamination from animal-processing plants by anaerobic thermophilic fermentation and by flesh fly digestion by U. Marchaim; A. Gelman; Y. Braverman (pp. 107-115).

There is currently no market in Israel for the large amounts of waste from fish- and poultry-processing plants. Therefore, this waste is incinerated, as part of the measures to prevent the spread of pathogens. Anaerobic methanogenic thermophilic fermentation (AMTF) of wastes from the cattle-slaughtering industry was examined previously, as an effective system to treat pathogenic bacteria, and in this article, we discuss a combined method of digestion by thermophilic anaerobic bacteria and by flesh flies, as a means of waste treatment. The AMTF process was applied to the wastes on a laboratory scale, and digestion by rearing of flesh fly (Phaenicia sericata) and housefly (Musca domestica) larvae on the untreated raw material was done on a small scale and showed remarkable weight conversion to larvae. The yield from degradation of poultry waste by flesh fly was 22.47% (SD=3.89) and that from fish waste degradation was 35.34% (SD=12.42), which is significantly higher than that from rearing houseflies on a regular rearing medium. Bacterial contents before and after thermophilic anaerobic digestion, as well as the changes in the chemical composition of the components during the rearing of larvae, were also examined.

Keywords: Thermophilic; anaerobic methanogenic thermophilic fermentation; fly larvae; poultry processing; fish processing; pathogenic bacteria

Pretreatment of swine wastewater using anaerobic filter by Ho Kang; Seo-Yeon Moon; Kyung-Sook Shin; Soon-Chul Park (pp. 117-126).

Efforts were made to assess the efficiency of an anaerobic filter packed with porous floating ceramic media and to identify the optimum operational condition of anaerobic filter as a pretreatment of swine wastewater for the subsequent biological removal of nitrogen and phosphorus. A stepwise decrease in hydraulic retention time (HRT) and an increase in organic loading rate (OLR) were utilized in an anaerobic filter reactor at mesophilic temperature (35°C). The optimum operating condition of the anaerobic filter was found to be at an HRT of 1 d. A soluble chemical oxygen demand (COD) removal efficiency of 62% and a total suspended solids removal efficiency of 39% at an HRT of 1 d were achieved with an OLR of 16.0 kg total COD/(m³·d), respectively. The maximum methane production rate approached 1.70 vol of biogas produced per volume of reactor per day at an HRT of 1 d. It was likely that the effluent COD/total Kjeldahl nitrogen ratio, of 22, the COD/total phosphorous ratio of 47, and the high effluent alkalinity >2500 mg/L as CaCO₃ of the anaerobic filter operated at an HRT of 1 d was adequate for the subsequent biological removal of nitrogen and phosphorus.

Keywords: Pretreatment; anaerobic filter; swine wastewater; nitrogen; phosphorus; anaerobic digestion

Anaerobic treatment of animal byproducts from slaughterhouses at laboratory and pilot scale by Mats Edström; Åke Nordberg; Lennart Thyselius (pp. 127-138).

Different mixtures of animal byproducts, other slaughterhouse waste (i.e., rumen, stomach and intestinal content), food waste, and liquid manure were codigested at mesophilic conditions (37°C) at laboratory and pilot scale. Animal byproducts, including blood, represent 70–80% of the total biogas potential from waste generated during slaughter of animals. The total biogas potential from waste generated during slaughter is about 1300 MJ/cattle and about 140 MI/pig. Fed-batch digestion of pasteurized (70°C, 1h) animal byproducts resulted in a fourfold increase in biogas yield (1.14L/g of volatile solids [VS]) compared with nonpasteurized animal bypproducts (0.31L/g of VS). Mixtures with animal byproducts representing 19–38% of the total dry matter were digested in continuous-flow stirred tank reactors at laboratory and pilot scale. Stable processes at organic loading rates (OLRs) exceeding 2.5g of VS/(L·d) and hydraulic retention times (HRTs) less than 40 d could be obtained with total ammonia nitrogen concentrations (NH₄−N+NH₃−N) in the range of 4.0–5.0 g/L. After operating one process for more than 1.5 yr at total ammonia nitrogen concentrations >4 g/L, an increase in OLR to 5 g of VS/(L·d) and a decrease in HRT to 22 d was possible without accumulation of volatile fatty acids.

Keywords: Animal byproducts; anaerobic treatment; animal waste; biogas; slaughterhouse waste; codigestion

Codigestion of proteinaceous industrial waste by R. Braun; E. Brachtl; M. Grasmug (pp. 139-153).

Organic wastes are increasingly collected source separated, thus requiring additional treatment or recovery capacities for municipal biowastes, organic industrial wastes, as well as agroindustrial byproducts. In this study, we demonstrate that anaerobic digestion is preferentially suited for high-water-containing liquid or pasty waste materials. We also evaluate the suitability of various organic wastes and byproducts as substrates for anaerobic digestion and provide a current status survey of codigestion. Biodegradation tests and estimations of the biogas yield were carried out with semisolid and pasty proteins and lipids containing byproducts from slaughterhouses; pharmaceutical, food, and beverage industries; distilleries; and municipal biowastes. Biogas yields in batch tests ranged from 0.3 to 1.36 L/g of volatile solids_added. In continuous fermentation tests, hydraulic retention times (HRTs) between 12 and 60 d, at a fermentation temperature of 35°C, were required for stable operation and maximum gas yield. Laboratory experiments were scaled up to full-scale codigestion trials in municipal and agricultural digestion plants. Up to 30% cosubstrate addition was investigated, using municipal sewage sludge as well as cattle manure as basic substrate. Depending on addition rate and cosubstrate composition, the digester biogas productivity could be increased by 80–400%. About 5–15% cosubstrate addition proved to be best suited, without causing any detrimental effects on the digestion process or on the further use of the digestate.

Keywords: Anaerobic digestion; codigestion; biowastes; industrial wastes; proteinaceous wastes; biogas

The reaction front hypothesis in solid-state digestion by Duncan J. Martin; Erzeng Xue (pp. 155-166).

An alternative mechanism for the anaerobic digestion of a bed of solids was recently proposed. A multizoned reaction front might form around a suitable body of seed material, then advance through the bed, within the solid phase. Such a solid-phase mechanism might coexist with liquid-phase digestion but one or the other of these two parallel mechanisms might generally be dominant. It is envisaged that solid-phase digestion would be favored by the presence of viable seed bodies: single particles of a suitable seed material above a minimum size or equivalent aggregates. A key determinant of the feasibility of this mechanism is expected to be the minimum viable size for a seed body (d _min). This would depend on the thickness of the reaction zones, some of which must initially be accommodated within the seed body. In this article, we present some theoretical estimates of d _min, which indicate a magnitude of 7–700 mm. Such values suggest that solid-phase digestion might be the norm in semi-dry waste digesters. Such digestion might be rare in unseeded landfills but it would appear likely that it could easily be initiated by suitable seeding.

Keywords: Anaerobic digestion; biomethanation; landfill; reaction front; rapidly solubilized organics; slowly solubilized organics; solid-phase digestion; seed body; digester

Two-step upflow anaerobic sludge bed system for sewage treatment under subtropical conditions with posttreatment in waste stabilization ponds by Lucas Seghezzo; Aníbal P. Trupiano; Viviana Liberal; Patrick G. Todd; María E. Figueroa; Marcelo A. Gutiérrez; Ana C. Da Silva Wilches; Martín Iribarnegaray; Raquel G. Guerra; Angélica Arena; Carlos M. Cuevas; Grietje Zeeman; Gatze Lettinga (pp. 167-180).

A pilot-scale sewage treatment system consisting of two upflow anaerobic sludge bed (UASB) reactors followed by five waste stabilization ponds (WSPs) in series was studied under subtropical conditions. The first UASB reactor started up in only 1 mo (stable operation, high chemical oxygen demand [COD] removal efficiency, low volatile fatty acids concentration in the effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm³/kg of COD_removed). Removal efficiencies up to 90% were obtained in the anaerobic steps at a hydraulic retention time of 6+4h (80% removal in the first step). Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobic steps and 99.98% in WSPs). COD balances over UASB reactors are provided. A minimum set of data necessary to build COD balances is proposed. Intermittent sludge washout was detected in the reactors with the COD balances. Sludge washout from single-step UASB reactors should be monitored and minimized in order to ensure constant complicance with discharge standards, especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions.

Keywords: Anaerobic treatment; sewage; subtropical regions; upflow anaerobic sludge bed reactors; waste stabilization ponds

Removal of chemical oxygen demand, nitrogen, and heavy metals using a sequenced anaerobic-aerobic treatment of landfill leachates at 10–30°C by Sergey Kalyuzhnyi; Marina Gladchenko; Andrey Epov; Vasu Appanna (pp. 181-195).

As a first step of treatment of landfill leachates (total chemical oxygen demand [COD]: 1.43–3.81 g/L; total nitrogen: 90–162 mg/L), performance of laboratory upflow anaerobic sludge bed reactors was investigated under mesophilic (30°C), submesophilic (20°C), and psychrophilic (10°C) conditions. Under hydraulic retention times (HRTs) of about 0.3 d, when the average organic loading rates (OLRs) were about 5 g of COD/(L·d), the total COD removal accounted for 81% (on average) with the effluent concentrations close to the anaerobic biodegradability limit (0.25 g of COD/L) for mesophilic and submesophilic regimes. The psychrophilic treatment conducted under an average HRT of 0.34 d and an average OLR of 4.22 g of ducted under an average HRT of 0.34 d and an average OLR of 4.22 g of COD/(L·d) showed a total COD removal of 47%, giving effluents (0.75 g of COD/L) more suitable for subsequent biologic nitrogen removal. All three anaerobic regimes used for leachate treatment were quite efficient for elimination of heavy metals (Fe, Zn, Cu, Pb, Cd) by concomitant precipitation in the form of insoluble sulfides inside the sludge bed. The application of aerobic/anoxic biofilter as a sole polishing step for psychrophilic anaerobic effluents was acceptable for elimination of biodegradable COD and nitrogen approaching the current standards for direct discharge of treated waste-water.

Keywords: Landfill leachate; upflow anaerobic sludge bed reactor; heavy metals; simultaneous anaerobic removal of ammonia and sulfate; aerobic-anoxic biofilter; nitrification; denitrification

Anaerobically treated wastewater in agricultural irrigation as an alternative for posttreatment in water-demanding zones by D. Jeison; R. Chamy; E. Salgado (pp. 197-206).

Agroindustries usually produce high amounts of wastewaters and are frequently located close to agricultural activities. Agricultural use of treated wastewaters therefore represents a unique opportunity to solve the problem of water supply for irrigation and disposal of treated water at the same time. This article is the result of collaborative work with the biggest Chilean pisco-(a distillated drink prepared from Muscatel wine) producing company at present. Experiments were conducted to establish anaerobic treatability of wastewaters and also irrigation properties of treated water. With the purpose of confirming laboratory results, a full-scale anaerobic plant was built, and treated water is being used to irrigate 3000 eucalypti. The results showed, at both laboratory and full scale, that anaerobic treatment is suitable for the treatment of pisco wastewater, and that nutrient content of treated water can be beneficial for plant growth, reducing the need for fertilizers.

Keywords: Pisco; anaerobic digestion; vinasses; irrigation; fertilization

Reductive decolorization of a textile reactive dyebath under methanogenic conditions by Eric J. Fontenot; Young Haeng Lee; Rosalyn D. Matthews; Guangxuan Zhu; Spyros G. Pavlostathis (pp. 207-225).

The objective of the present study was to assess the biological decolorization of an industrial, spent reactive dyebath and its three dye components (Reactive Blue 19 [RB 19], Reactive Blue 21 [RB 21], and Reactive Red 198 [RR 198]) under methanogenic conditions. Using a mixed, methanogenic culture, batch assays were performed to evaluate the rate and exten of color removal as well as any potential toxic effects. Overall, a high rate and extent of color removal (>10 mg/[L·h] and 88%, respectively) were observed in cultures amended with either RB19 (an anthraquinone dye) or spent dyebath at an initial dye concentration of 300 mg/L (expressed as RB 19 equivalent) and 30 g/L of NaCl. Inhibition of acidogenesis and, to a larger degree, of methanogenesis resulting in accumulation of volatile fatty acids was observed in both RB 19- and spent dyebath-amended cultures. RB 21 (a phthalocyanine dye) and RR 198 (an azo dye) tested at an initial concentration of 300 mg/L did not result in any significant inhibition of the mixed methanogenic culture. Based on results obtained with cultures amended with RB 19 with and without NaCl, as well as a control culture amended with 30 g/L of NaCl, salt was less inhibitory than either RB 19 or the dyebath. Therefore, the toxic effect of the spent dyebath is at least partially attributed to its major dye component RB 19 and NaCl. Further testing of the effect of RB 19 decolorization products on the methanogenic activity in the absence of NaCl demonstrated that these products are much less inhibitory than the parent dye. Although color removal occurred despite the severe culture inhibition, biological decolorization of full-strength reactive spent dyebaths using methanogenic cultures in a repetitive, closed-loop system is not deemed feasible. For this reason, a fermentative and halotolerant culture was developed and successfully used in our laboratory for the decolorization of industrial reactive dyebaths with 100 g/L of NaCl.

Keywords: Anthraquinone dyes; decolorization; methanogenesis; phthalocyanine dyes; reactive textile dyes; salt; toxicity

Electron beam pretreatment of sewage sludge before anaerobic digestion by Kyung-Sook Shin; Ho Kang (pp. 227-239).

The pretreatment of waste-activated sludge (WAS) by electron beam irradiation was studied in order to improve anaerobic sludge digestion. The irradiation dose of the electron beam was varied from 0.5 to 10 kGy. Batch and continuous-flow stirred tank reactors (CFSTRs) were operated to evaluate the effect of the electron beam pretreatment on anaerobic sludge digestion. Approximately 30–52% of the total chemical oxygen demand (COD) content of the WAS was solubilized within 24 h after electron beam irradiation. A large quantity of soluble COD, protein, and carbohydrates leached out from cell ruptures caused by the electron beam irradiation. Volatile fatty acids production from the irradiated sludge was approx 90% higher than that of the unirradiated sludge. The degradation of irradiated sewage sludge was described by two distinct first-order decay rates (k ₁ and k ₂). Most initial decay reaction accelerated within 10 d, with an average k ₁ of 0.06/d for sewage sludge irradiated at all dosages. The mean values for the long-term batch first-order decay coefficient (k ₂) were 0.025/d for irradiated sewage sludge and 0.007/d for unirradiated sludge. Volatile solids removal efficiency of the control reactor fed with unirradiated sewage sludge at a hydraulic retention time (HRT) of 20 d was almost the same as that of the CFSTRs fed with irradiated sludge at an HRT of 10 d. Therefore, disintegration of sewage sludge cells using electron beam pretreatment could reduce the reactor solid retention time by half.

Keywords: Sewage sludge; electron beam; sludge disintegration; biochemical acid potential test; first-order decay rate; anaerobic digestion

Anaerobic waste stabilization ponds by G. E. Alexiou; D. D. Mara (pp. 241-252).

Waste stabilization ponds (WSP) have been used extensively all over Europe over the last 50 yr for the treatment of municipal and industrial wastewaters. Models presented in manuals should be used only for guidance, and local experience from pilot and full-scale plants of a particular pond type is extremely valuable. Anaerobic WSP are single-stage, continuous-flow, anaerobic reactors operating at ambient temperatures and low volumetric organic loading as a pretreatment method. This article presents a literature review on the different available operational parameters of anaerobic ponds and exmaples from full-scale plant performance world-wide. On a wastewater management scheme, involving reuse for agriculture, the zero-energy demand of a waste stabilization pond series for the effective removal of organic and microbiological loading under existing legislation and guidelines will remain a valuable tool for sustainable development.

Keywords: Waste stabilization ponds; anaerobic ponds; operational parameters; reuse

Combined biologic (anaerobic-aerobic) and chemical treatment of starch industry wastewater by Vladimir Sklyar; Andrey Epov; Marina Gladchenko; Dmitrii Danilovich; Sergey Kalyuzhnyi (pp. 253-262).

A combined biologic and chemical treatment of high-strength (total chemical oxygen demand [COD_tot] up to 20 g/L), strong nitrogenous (total N up to 1 g/L), and phosphoric (total P up to 0.4 g/L) starch industry wastewater was investigated at laboratory-scale level. As a principal step for COD elimination, upflow anaerobic sludge bed reactor performance was investigated at 30°C. Under hydraulic retention times (HRTs) of about 1 d, when the organic loading rates were higher than 15g of COD/(L·d), the COD_tot removal varied between 77 and 93%, giving effluents with a COD/N ratio of 4–5∶1, approaching the requirements of subsequent denitrification. The activated sludge reactor operating in aerobic-anoxic regime (HRT of about 4 d, duration of aerobic and anoxic phases of 30 min each) was able to remove up to 90% of total nitrogen and up to 64% of COD_tot from the anaerobic effluents under 17–20°C. The coagulation experiments with Fe(III) showed that 1.4 mg of resting hardly biodegradable COD and 0.5 mg of phosphate (as P) could be removed from the aerobic effluents by each milligram of iron added.

Keywords: Activated sludge reactor; coagulation; nutrient removal; starch wastewater; upflow anaerobic sludge bed reactor

Production and energetic use of biogas from energy crops and wastes in Germany by Peter Weiland (pp. 263-274).

The production of biogas for reducing fossil CO₂ emissions is one of the key strategic issues of the German government and has resulted in the development of new process techniques and new technologies for the energetic use of biogas. Progress has been made in cultivating energy crops for biogas production, in using new reactor systems for anaerobic digestion, and in applying more efficient technologies for combined heat and power production. Recently, integration of fuel cells within the anaerobic digestion process was started, and new technologies for biogas upgrading and conversion to hydrogen were tested. This article describes the trends in Germany for achieving more efficient energy production.

Keywords: Biogas production; biogas processes; digestion systems; energy crops; fuel cells

Development and Use of an economic evaluation model to assess establishment of local centralized rural biogas plants in Greece by D. Georgakakis; N. Christopoulou; A. Chatziathanassiou; T. Venetis (pp. 275-284).

An economic evaluation model was developed in the Laboratory of Agricultural Structures (LAS) of the Agricultural University of Athens—the Modified Basic Economic Evaluation Model (MBEEM). This model is an improved version of the original Basic Economic Evaluation Model, available in LAS, and it is used to assess the cost-effectiveness of biogas production systems. Because of the parameters involved, a computer model was developed to facilitate the application of the MBEEM. The model was used in this work to determine the cost-effective size of a local centralized biogas production system fed with pig wastes.

Keywords: Pig wastes; centralized biogas plant; economic evaluation model

Aerobic and anaerobic microbial degradation of poly-β-hydroxybutyrate produced by Azotobacter chroococcum by G. A. Bonartseva; V. L. Myshkina; D. A. Nikolaeva; M. V. Kevbrina; A. Y. Kallistova; V. A. Gerasin; A. L. Iordanskii; A. N. Nozhevnikova (pp. 285-301).

Food industry wastewater served as a carbon source for the synthesis of poly-β-hydroxybutyrate (PHB) by Azotobacter chroococcum. The content of polymer in bacterial cells grown on the raw materials reached 75%. PHB films were degraded under aerobic, microaerobic, and anaerobic conditions in the presence and absence of nitrate by microbial populations of soil, sludges from anaerobic and nitrifying/denitrifying reactors, and sediment from a sludge deposit site. Changes in molecular mass, crystallinity, and mechanical properties of PHB were studied. Anaerobic degradation was accompanied by acetate formation, which was the main intermediate utilized by denitrifying bacteria or methanogenic archaea. On a decrease in temperature from 20 to 5° C in the presence of nitrate, the rate of PHB degradation was 7.3 times lower. Under anaerobic conditions and in the absence of nitrate, no PHB degradation was observed, even at 11°C. The enrichment cultures of denitrifying bacteria obtained from soil and anaerobic sludge degraded PHB films for a short time (3–7 d). The dominant species in the enrichment culture from soil were Pseudomonas fluorescens and Pseudomonas stutzeri. The rate of PHB degradation by the enrichment cultures depended on the polymer molecular weight, which reduced with time during biodegradation.

Keywords: Aerobic, microaerobic, and anaerobic conditions; Azotobacter chroococcum ; denitrification; denitrifying microorganisms; methanogenesis; microbial degradation; poly-β-hydroxybutyrate

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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.109, #1-3)

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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.109, #1-3)