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The aim of this study was the performance evaluation of anaerobic digestion of dairy wastewater in a multi-section horizontal flow reactor (HFAR) equipped with microwave and ultrasonic generators to stimulate biochemical processes. The effects of increasing organic loading rate (OLR) ranging from 1.0 g chemical oxygen demand (COD)/L·d to 4.0 g COD/L·d on treatment performance, biogas production, and percentage of methane yield were determined. The highest organic compounds removals (about 85% as COD and total organic carbon—TOC) were obtained at OLR of 1.0–2.0 g COD/L·d. The highest biogas yield of 0.33 ± 0.03 L/g COD removed and methane content in biogas of 68.1 ± 5.8% were recorded at OLR of 1.0 g COD/L·d, while at OLR of 2.0 g COD/L·d it was 0.31 ± 0.02 L/COD removed and 66.3 ± 5.7%, respectively. Increasing of the OLR led to a reduction in biogas productivity as well as a decrease in methane content in biogas. The best technological effects were recorded in series with an operating mode of ultrasonic generators of 2 min work/28 min break. More intensive sonication reduced the efficiency of anaerobic digestion of dairy wastewater as well as biogas production. A low nutrient removal efficiency was observed in all tested series of the experiment, which ranged from 2.04 ± 0.38 to 4.59 ± 0.68% for phosphorus and from 9.67 ± 3.36 to 20.36 ± 0.32% for nitrogen. The effects obtained in the study (referring to the efficiency of wastewater treatment, biogas production, as well as to the results of economic analysis) proved that the HFAR can be competitive to existing industrial technologies for food wastewater treatment.

The aim of this study was to determine the effects on methane production of the addition of microalgae biomass of Arthrospira platensis and Platymonas subcordiformis to the common feedstock used in agricultural biogas plants (cattle manure, maize silage). Anaerobic biodegradability tests were carried out using respirometric reactors operated at an initial organic loading rate of 5.0 kg volatile solids (VS)/m3, temperature of 35°C, and a retention time of 20 days. A systematic increase in the biogas production efficiency was found, where the ratio of microalgae biomass in the feedstock increased from 0% to 40% (%VS). Higher microalgae biomass ratio did not have a significant impact on improving the efficiency of biogas production, and the biogas production remained at a level comparable with 40% share of microalgae biomass in the feedstock. This was probably related to the carbon to nitrogen (C/N) ratio decrease in the mixture of substrates. The use of Platymonas subcordiformis ensured higher biogas production, with the maximum value of 1058.8 ± 25.2 L/kg VS. The highest content of methane, at an average concentration of 65.6% in the biogas produced, was observed in setups with Arthrospira plantensis biomass added at a concentration of between 20%–40% to the feedstock mixture.

The aim of the study was to determine the use of digestate from anaerobic digestion of dairy wastewater as a culture medium for microalgae to obtain bio-oil. The experiments were conducted at a small scale in a closed raceway pond. The efficiency of the microalgae biomass production, the digestate treatment efficiency as well as the content and properties of the bio-oil obtained from the microalgal cells were analyzed. The produced biomass concentration was about 3000 ± 10.5 mg dry biomass/L, with an average growth rate of 160 ± 6.6 mgdm/L·d. The efficiency of organic compound and nutrient removal was above 90%. The bio-oil content in the biomass was about 20%. Based on the results of the study, a concept for technical-scale technology was developed.

The aim of the study was to determine the impact of the constant magnetic field (CMF) application on the effectiveness of anaerobic digestion of algal biomass. The highest yield of biogas in the range of 448.9 L/kg volatile solids (VS) to 456.6 L/kg VS was observed in the variants, in which the retention time in the CMF-exposed area ranged from 144 to 216 min/d. Under these conditions, the concentration of methane in the biogas was nearly 65.0%. The increase in the contact time of the fermentation medium with the CMF-exposed area had a significant impact of reducing the effectiveness of anaerobic digestion. The lowest biodegradation was observed when the retention time was 432 min/d. Under such condition, 281.1 L of biogas/kg VS with methane content of 41.8% was obtained. A correlation between the time of exposure to CMF and the values of parameters characterizing the methane production was found.

Purpose This study investigated the chemical characteristics and anaerobic digestion of Chlorella sp. microalgae cultivated on various anaerobic digestion effluents (ADEs) as a nutrient medium. Chlorella sp. was grown in anaerobically digested effluent of dairy wastewater (DW), municipal wastewater sludge (WS), maize silage and swine slurry, and cattle manure (CM). Methods To evaluate the anaerobic biodegradability of harvested biomass, 20-days batch anaerobic digestion experiments were used. Results It was found that a nutrient medium directly affected nitrogen concentration in the cultivated biomass, as well as the C/N ratio value which ranged 7.2-12.9. Higher C/N ratio of the Chlorella sp. cultivated on DW and WS significantly enhanced the methane production, which was 241 ± 5.5 mL CH 4 /g VS and 267 ± 10.9 mL CH 4 /g VS, respectively. The highest biogas production rate of 61.28 ± 2.7 mL/g VSÁd and methane concentration in biogas of 69.7 ± 4.1 % were obtained during the digestion of Chlorella sp. biomass cultivated on WS.Conclusions These results proved the applicability of ADEs as a nutrient medium for Chlorella sp. cultivation and the impact of a nutrient source on C/N ratio in harvested biomass, which subsequently affected the biogas/ methane yield.

The influence of ultrasonic pretreatment with specific energy input ranging from 25 to 550 kJ/kg volatile solids on the mixture of Sida hermaphrodita (L.) Rusby mixed with cattle manure disintegration and subsequent anaerobic digestion was assessed. The pretreatment process led to significant increase in the biomass solubility by 21.9% as chemical oxygen demand and enhanced biogas yield by 157% (567.1 L biogas/kg volatile solids) when the specific energy input was from 200 to 550 kJ/kg. However, only pretreatments where ultrasound was applied at 25-50 kJ/kg led to positive net energy gain, indicating that the biomass processing with this method does not always compensate the energy consumption for irradiation.

This study focuses on the exploitation of the two‐stage continuous fermentation process for biohydrogen and biomethane production from whey permeate. Mesophilic fermentative biohydrogen production was investigated at a constant hydraulic retention time (HRT) of 24 h and organic loading rates (OLRs) of 20, 25, 30, and 35 kg COD/m3·d. The hydrogenogenic reactor was successfully operated at OLR of 30 kg COD/m3·d when the proportion of hydrogen in biogas, volumetric productionrsquo rate of hydrogen, and hydrogen yield reached the maximum values of 44.6 ± 0.8%, 5.26 ± 0.15 L H2/d, and 4.19 mol H2/kg CODremoved, respectively. The effluent from hydrogenogenic reactor was further digested to biogas in the second reactor operated at a HRT of 3 d and variable OLR in the range of 0.9–1.9 kg COD/m3·d. Maximum biogas production rate, volumetric production rate of methane and methane yield were 16.90 ± 0.6 L/d, 11.95 ± 0.6 L CH4/d, and 0.12 m3 CH4/kg CODadded. The total chemical oxygen demand elimination from whey permeate reached 98% in a two‐stage process. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 1411–1418, 2014