Kinetic study of mesophilic anaerobic digestion of pulp & paper sludge

Anaerobic digestion of pulp and paper sludge (PPS) and monosodium glutamate waste liquor (MGWL) was studied in completely stirred tank reactors (CSTR) at 37 ± 2 °C. This work focused on the effect of increased organic loading rate (OLR) on the methane production in long-term experiments. For OLR in the range of (1.5-5.0) kg m⁻³ d⁻¹ based on VS fed, VFA and SCOD concentrations decreased for the first 10 days and then kept stable at about 2.3 kg m⁻³ and 4.0 kg m⁻³ respectively until to the critical OLR of 5.0 kg m⁻³ d⁻¹; and the methane generation rate enhanced to 0.838 m³ m⁻³ d⁻¹ during this period until to the reactor failure. Additionally, reaction rate constant k and sludge retention time (SRT) are described on the basis of a mass balance in a CSTR followed a first order kinetic equation. In the present study, values for y_m and k were obtained as 0.733 m³ kg⁻¹ of removed VS and 0.07 d⁻¹, respectively. The simple model can apply for dimensioning a CSTR digesting of organic wastes from pulp and paper industries, food processing industries, sewage treatment plants or biogas crops.     

Effects of solid retention time on anaerobic digestion of dewatered-sewage sludge in mesophilic and thermophilic conditions

Anaerobic digestion of dewatered-sewage sludge using continuous stirred tank reactors (CSTRs) in duplicates was evaluated under thermophilic (50 °C) and mesophilic (37 °C) conditions over a range of nine solid retention times (SRTs). The 35- and 30-day SRTs were designed to simulate a full-scale plant operation while 25-, 20-, 15- and 12-day SRTs were planned to evaluate process performance at the various SRTs. The 9-, 5- and 3-day SRTs were performed to push the reactors to extend their degradation capacity and test the threshold for process imbalance. The corresponding organic loading rates (OLR) varied from 1.6 to 20.5 kg VS m^?3 day^?1. Biogas production rate could be tripled when the SRT was shortened from 30 to 12 days and more than doubled from 35- to 15-day SRT because of a concomitant increase in OLR. In general, higher biogas productivity was realized under thermophilic, but methane yields were comparable due to the higher methane content in the biogas under mesophilic digestion. The methane content in biogas fluctuated between 55 and 65% and the methane yield ranged from 0.314 to 0.348 Nm³ CH₄ kg VS_added^?1 day^?1 for both thermophilic and mesophilic digestion. The VS-reduction at 12- and 15-day SRT ranged from 45 to 52% and there was no accumulation of VFAs. Increasing concentrations of VFAs, decreasing concentration of partial alkalinity and decrease in pH were noted as signs of reactor instability. Process imbalance started at 9-day SRT, souring of the reactors, cell wash-out and foaming was noted as the principal causes of process failure under both thermophilic and mesophilic conditions. This study projected the possibility of using CSTRs in treating dewatered-sewage sludge at a shorter SRT to achieve reasonable biogas production and VS-reduction without encountering adverse operation conditions as foaming and wash-out of cells.     

Hydrogen bioproduction with anaerobic bacteria consortium from brewery wastewater

Biohydrogen production is a cheap and clean way to obtain hydrogen gas. In subtropical countries such as Brazil the average temperatures of 27 °C can favor the hydrogen producing bacteria growth. A mixed culture was obtained from a subtropical sludge treating brewery wastewater and anaerobic batch reactors were fed with glucose, sucrose, fructose and xylose in low concentrations (2.0, 5.0 and 10.0 g L⁻¹) at 37 °C, initial pH 5.5 and headspace with N₂ (99%) to maintain the anaerobic conditions. The inoculum was a subtropical granulated sludge from UASB (Upflow Anaerobic Sludge Blanket) reactor treating brewery wastewater. The higher H₂ yields were obtained in reactors operated with 2 and 5 g L⁻¹ of fructose and they were 1.5 mol H₂ mol⁻¹ of fructose and 1.3 mol H₂ mol⁻¹ of sucrose, respectively. The volatile fatty acids (VFA) generated at the end of operation were, predominantly, butyric and acetic acid, indicating the favoring of the metabolic route of hydrogen generation by the consortium of anaerobic bacteria from the brewery wastewater. Biomolecular analyses revealed the predominance of hydrogen producing bacteria from Firmicutes phylum distributed in the families Streptococcaceae, Veillonellaceae and uncultured bacteria. These results confirm future applications of subtropical sludges with agroindustrial wastewaters containing low concentrations of sugars on hydrogen generation.     

A bench scale study of fermentative hydrogen and methane production from food waste in integrated two-stage process

A two-stage fermentation process combining hydrogen and methane production for the treatment of food waste was investigated in this paper. In hydrogen fermentation reactor, the indigenous mixed microbial cultures contained in food waste were used for hydrogen production. No foreign inoculum was used in the hydrogen fermentation stage, the traditional heat treatment of inoculum was not applied either in this bench scale experiment. The effects of the stepwise increased organic loading rate (OLR) and solid retention time (SRT) on integrated two-stage process were investigated. At steady state, the optimal OLR and SRT for the integrated two-stage process were found to be 22.65 kg VS/m³ d (160 h) for hydrogen fermentation reactor and 4.61 (26.67 d) for methane fermentation reactor, respectively. Under the optimum conditions, the maximum yields of hydrogen (0.065 m³ H₂/kg VS) and methane (0.546 m³ CH₄/kg VS) were achieved with the hydrogen and methane contents ranging from 29.42 to 30.86%, 64.33 to 71.48%, respectively. Biodegradability analysis showed that 5.78% of the influent COD was converted to the hydrogen in H₂-SCRD and 82.18% of the influent COD was converted to the methane in CH₄-SCSTR under the optimum conditions.     

Mesophilic and thermophilic anaerobic co-digestion of waste activated sludge and source sorted biowaste in pilot- and full-scale reactors

The paper presents the results of a pilot- and full-scale experimental campaign on the anaerobic co-digestion of waste activated sludge and biowaste both in mesophilic and thermophilic conditions. The study demonstrated the possibility to increase the specific biogas production from 0.34 to 0.49 m³/kgTVS and the gas production rate from 0.53 to 0.78 m³per m³ of reactor per day changing the reactor temperature from the mesophilic (37 °C) to the thermophilic (55 °C) range. The experimental work was carried out at pilot-scale, and the results match the full-scale behaviour. Ammonia nitrogen recycled from the anaerobic digestion section to the wastewater treatment plant accounted for about 4% of the total nitrogen loading. Digestate characteristics in terms of biological stability and heavy metals content suggested the opportunity of a short time post-aerobic stabilisation, leading to a high quality compost product.     

Estimating microbial electrolysis cell (MEC) investment costs in wastewater treatment plants: Case study

Microbial electrolysis represents a new approach for harnessing the energy contained in the organic matter of wastewater. However, before this approach can be implemented on a practical basis, a cost-effective manufacturing process for microbial electrolysis cells (MECs) must be developed. The objective of this study is to estimate an acceptable purchase cost of an MEC reactor for a domestic wastewater treatment plant. We estimate that for a full-scale MEC operating at a current density of 5 A m_a⁻² (amperes per square meter of anode) and an energy consumption of 0.9 kWh kg-COD⁻¹ (kilowatt-hour per kg of removed chemical oxygen demand (COD)), a cost of €1220 m_a⁻³ (euro per m³ of anodic chamber) can be established as a target purchase cost at which a break-even point is reached after 7 years.     

Hydrogen production from alcohol wastewater with added fermentation residue by an anaerobic sequencing batch reactor (ASBR) under thermophilic operation

The objective of this study was to investigate the enhancement of hydrogen production from alcohol wastewater by adding fermentation residue using an anaerobic sequencing batch reactor (ASBR) under thermophillic operation (55 °C) and at a constant pH of 5.5. The digestibility of the added fermentation residue was also evaluated. For a first set of previous experiments, the ASBR system was operated to obtain an optimum COD loading rate of 50.6 kg/m³ d of alcohol wastewater without added fermentation residue and the produced gas contained 31% H₂ and 69% CO₂. In this experiment, the effect of added fermentation residue (100–1200 mg/l) on hydrogen production performance was investigated under a COD loading rate of 50.6 kg/m³ d of the alcohol wastewater. At a fermentation residue concentration of 1000 mg/l, the produced gas contained 40% H₂ and 60% CO₂ without methane and the system gave the highest hydrogen yield and specific hydrogen production rate of 128 ml/g COD removed and 2880 ml/l d, respectively. Under thermophilic operation with a high total COD loading rate (51.8 kg/m³ d) and a short HRT (21 h) at pH 5.5, the ASBR system could only break down cellulose (41.6%) and hemicellulose (21.8%), not decompose lignin.     

Effect of organic loading rate and solids retention time on microbial population during bio-hydrogen production by dark fermentation in large lab-scale

The experimental investigation aimed at the study of the microbial population during the continuous operation of a complete mixed reactor in large lab-scale (30 L) by variation of the Organic Loading Rate (OLR) and Sludge Retention Time (SRT) ranging from 10 g sucrose/(L?d) to 30 g/(L?d) and from 12 h to 48 h respectively. H₂ yield reached to 1.72 mol H₂/mol hexose for HRT = 1.6 d and OLR = 20 g sucrose/(L?d). In each phase the dominant microbial genera were identified by sequencing after a Polymerase Chain Reaction (PCR) with universal primers for the domains of Archaea and Eubacteria and specific for Clostridium species and genetic material isolation by Denaturing Gradient Gel Electrophoresis (PCR-DGGE). The phylogenetic analyses showed that hydrogen producing Clostridium species could be affiliated in all experimental phases. Other dominant genera were affiliated mainly to Ethanoligenes harbinense and uncultured Prevotella and Selonomonas species. Bio-hydrogen production was associated to a mixed butyric/ethanol type fermentation facilitated mainly by Clostridium tyrobutyricum and E. harbinense in the presence of lactate as intermediate metabolic product.     

Promoting direct interspecies electron transfer for methane production in bioelectrochemical anaerobic digestion: Impact of electrode surface area and switching circuit

The bioelectrochemical enhancement of direct interspecies electron transfer (DIET) for methane production was investigated in a UASB reactor under different electrode surface areas. The specific methane production rate is stabilized at 316.7 mL/g COD in the bioelectrochemical UASB (BUASB) reactor with an electrode surface area of 10 m²/m³, which is significantly higher than the 216.8 mL/g COD of the UASB reactor. The electroactive bacteria, involved in the DIET for methane production, is signifianctly increased in the BUASB reactor. When the electrode surface area is expanded to (20 and 30) m²/m³, the specific methane production rates in the BUASB reactor are further increased to (358.4 and 361.0) mL/g COD, respectively (p-value > 0.05). The theoretical methane production from the electrode surface is approximate 3.1% of the total methane production in all BUASB reactors, and the bioelectrochemical methane production is mainly attributed to the biological DIET pathway (54%) in the bulk solution. The BUASB reactor at the electrode surface area of 20 m²/m³ showes better performance according to the methane production, process stability, and enrichment of electroactive microorganisms. The bioelectrochemical system provides a new platform that can dramatically improve the performance of UASB process for treating brewery wastewater.     

Treatment of dairy wastewater using anaerobic and solar photocatalytic methods

The present study was aimed to treat the dairy wastewater by using anaerobic and solar photocatalytic oxidation methods. The anaerobic treatment was carried out in a laboratory scale hybrid upflow anaerobic sludge blanket reactor (HUASB) with a working volume of 5.9 L. It was operated at organic loading rate (OLR) varying from 8 to 20 kg COD/m³ day for a period of 110 days. The maximum loading rate of the anaerobic reactor was found to be 19.2 kg COD/m³ day and the corresponding chemical oxygen demand (COD) removal at this OLR was 84%. The anaerobically treated wastewater at an OLR of 19.2 kg COD/m³ day was subjected to secondary solar photocatalytic oxidation treatment. The optimum pH and catalyst loading for the solar photochemical oxidation was found to be 5 and 300 mg/L, respectively. The secondary solar photocatalytic oxidation using TiO₂ removed 62% of the COD from primary anaerobic treatment. Integration of anaerobic and solar photocatalytic treatment resulted in 95% removal of COD from the dairy wastewater. The findings suggest that anaerobic treatment followed by solar photo catalytic oxidation would be a promising alternative for the treatment of dairy wastewater.     

Electricity generation by microbial fuel cells fuelled with wheat straw hydrolysate

Electricity production from microbial fuel cells fueled with hydrolysate produced by hydrothermal treatment of wheat straw can achieve both energy production and domestic wastewater purification. The hydrolysate contained mainly xylan, carboxylic acids, and phenolic compounds. Power generation and substrate utilization from the hydrolysate was compared with the ones obtained by defined synthetic substrates. The power density increased from 47 mW m⁻² to 148 mW m⁻² with the hydrolysate:wastewater ratio (R_HW in m³ m⁻³) increasing from 0 to 0.06 (corresponding to 0-0.7 g dm⁻³ of carbohydrates). The power density with the hydrolysate was higher than the one with only xylan (120 mW m⁻²) and carboxylic acids as fuel. The higher power density can be caused by the presence of phenolic compounds in the hydrolysates, which could mediate electron transport. Electricity generation with the hydrolysate resulted in 95% degradation of the xylan and glucan. The study demonstrates that lignocellulosic hydrolysate can be used for co-treatment with domestic wastewater for power generation in microbial fuel cells.     

Start-up of an UASB reactor treating potato-starch wastewater using an alkalimetric follow-up procedure

Monitoring of volatile fatty acids (VFA) by gas chromatography or hydrogen with specific electrodes is used for the determination of instability in anaerobic reactors. However, such methods are not normally applied in full-scale reactors due to the need for expensive equipment. A two end-point alkalimetric method has been proposed in the literature for the follow-up and control of anaerobic digesters. This paper deals with results of the start-up and operation of a laboratory UASB (Upflow Anaerobic Sludge Blanket) reactor (5.61) treating potato-starch wastewater, where such an alkalimetric method was simultaneously used and compared with gas-chromatography VFA monitoring.     

Novel design of a multitube microbial fuel cell (UM2FC) for energy recovery and treatment of membrane concentrates

A two-stage treatment process, consisting of a flat sheet membrane system and a novel upflow multitube microbial fuel cell (UM²FC), was investigated to simultaneously treat concentrate streams—as well as produce electricity. This study tested the treatment of the retained part (i.e membrane concentrate) of the membrane process and electricity production using an air-cathode UM²FC inoculated with sediment sample collected from Golden Horn, Istanbul. The electrochemical behaviors were investigated using electrochemical methods to identify how membrane concentrates effects the reactor performance. The treatment of domestic wastewater was performed using a lab-scale cross-flow filtration apparatus with a UH050 membrane and the chemical oxygen demand (COD) removal efficiency as a result of membrane treatment was 87%. Then the UM²FC was fed sequentially from the feed tank when desired retained ratios (25% and 50%) observed. The maximum power density obtained was 25.138 mW m⁻² in the 50% concentrate or a volume concentration ratio (VCR) of 2 fed UM²FC which was 244% higher than that achieved using raw wastewater (7.303 mW m⁻²) and COD removal was >65% in UM²FC. The contribution of different resistances such as ohmic, charge transfer and mass transfer resistances of the reactor under different stages was ascertained through the measurements using electrochemical impedance spectroscopy (EIS) and the results showed that an increasing organic loading reduced the internal resistance and enhanced power. On the whole, study reported new findings such as a new treatment technology for membrane concentrate treatment and gives insight to literature on reactor design.     

Efficiency assessment of a photo electrochemical chloralkali process for hydrogen and sodium hydroxide production

In present study, a new reactor configuration is developed which integrates photochemical hydrogen production with an electrochemical chloralkali process. The effects of different parameters on rate of hydrogen, chlorine and sodium hydroxide production are experimentally examined and discussed. The parameters include applied voltage, varied from 4 V to 5 V, amount of catalyst, varied from 1 g/425 mL to 4 g/425 mL, and light intensity, varied from 20 W/m² to 55 W/m². Factorial design of experiments is applied and an analysis of variance (ANOVA) is used to analyze the experimental results. Energy and exergy efficiencies are also examined. An optimization study is performed to find the optimal catalyst concentration. An optimized catalyst concentration in salty water is used to examine its effect on the rate of hydrogen production.     

Bioconversion of crude glycerol from waste cooking oils into hydrogen by sub-tropical mixed and pure cultures

This study compared the biohydrogen generation by sub-tropical mixed and pure cultures from the crude glycerol from the biodiesel production using waste cooking oils (WCO). The crude glycerol was pretreated by pH adjustment. The mixed culture was obtained from a subtropical granular sludge of the UASB (Upflow Anaerobic Sludge Blanket) reactor used in the treatment of vinasse from sugarcane of ethanol and sugar industry. It was heat treated in order to inactivate hydrogen-consuming bacteria, which was identified by Illumina MiSeq Sequencing with a relative abundance of 97.96% Firmicutes Philum, 91.81% Clostridia Class and 91.81% Clostridiales Order. The pure culture was isolated from a sub-tropical granular sludge from UASB reactor of treating brewery wastewater and identified as Enterobacter sp. (KP893397). Two assays were carried in anaerobic batch reactors in order to verify the hydrogen production from crude glycerol bioconversion with: (I) mixed culture and (II) pure culture. The experiments were conducted at 37 °C, initial pH of 5.5 for assay I and 7.0 for assay II, with 20 g COD L⁻¹ of crude glycerol. The crude glycerol consumption was 56.2% and 88.0% for the assay I and II, respectively. The hydrogen yields were 0.80 moL H₂ mol⁻¹ glycerol for the assay I and 0.13 moL H₂ mol⁻¹ glycerol for the assay II. Enterobacter sp. preferred the reductive metabolic route, generating 1460.0 mg L⁻¹ of 1,3-propanediol, and it showed to be more sensitive in the presence of methanol from crude glycerol than mixed culture that preferred the oxidative metabolic route with biohydrogen generation. The mixed culture was more able to generate H₂ than pure culture from the crude glycerol coming from the biodiesel production using WCO.     

Experimental study of a solar desalination pond as second stage in proposed zero discharge desalination process

This work represents the efficiency of a solar desalination pond as a second stage of proposed zero discharge desalination processes to reach fresh water and also concentrated brine from the effluent wastewater of the desalination unit of Mobin petrochemical complex. So a solar desalination pond is constructed after a pretreatment unit to concentrate the softened wastewater to about 20 wt%. The concentrated wastewater is as a suited feed for a forced circulation crystallizer. During one year, the effects of major parameters such as ambient temperature and solar insolation rate are investigated, experimentally. specific gravity in each layer of concentrated brine wastewater is evaluated. Also, evaporation rates are calculated theoretically and are verified by experimental data. Theoretical values predict evaporation rate accurately. Results show good agreement with experimental data. According to results, maximum evaporation rate is 5 l/m² day when the insolation rate is about 24,602 kJ/m² day Solar energy absorption factor on June is max. Also, experimental results show the best proposed time to gain highest thermal energy is on spring therefore performance efficiency of solar desalination pond promote on spring comparing with the other months. Extracted data for specific gravity prove the bottom of solar desalination pond, layer 1, is best zone for energy saving and energy utilization.Also, theoretical values of evaporation rate are calculated according to measured temperatures and related mass conservation equation. Comparison between theoretical and experimental values shows dusty weather, humidity and wind velocity affects on heat transfer coefficients approximately. So, deviations between theoretical data and measured values can be explained. Results show good agreements with experimental data.     

Hydrogen and methane production in extreme thermophilic conditions in two-stage (upflow anaerobic sludge bed) UASB reactor system

Two-stage hydrogen and methane production in extreme thermophilic (70 °C) conditions was demonstrated for the first time in UASB-reactor system. Inoculum used in hydrogen and methane reactors was granular sludge from mesophilic internal circulation reactor and was first acclimated for extreme thermophilic conditions. In hydrogen reactor, operated with hydraulic retention time (HRT) of 5 h and organic loading rate (OLR) of 25.1 kg COD/m³/d, hydrogen yield was 0.73 mol/mol glucose_added. Methane was produced in second stage from hydrogen reactor effluent. In methane reactor operated with HRT of 13 h and OLR of 7.8 kg COD/m³/d, methane yield was 117.5 ml/g COD_added. These results prove that hydrogen and methane can be produced in extreme thermophilic temperatures, but as batch experiments confirmed, for methane production lower temperature would be more efficient.     

Optimal operational conditions for biohydrogen production from sugar refinery wastewater in an ASBR

The performance of biohydrogen production in an anaerobic sequencing batch reactor (ASBR) was evaluated with respect to variations in the key operational parameters – pH, hydraulic retention time HRT, and organic loading rate OLR using sugar refinery wastewater as substrate. Analysis of variance (ANOVA) indicated HRT had less significant influence on hydrogen content and yield in comparison to pH and OLR, whereas OLR has much impact on hydrogen production rate. Taxonomic analysis results showed that diverse bacterial species contributed to hydrogen production and the dominant species in the bioreactor were governed by all operational parameters. Even without pretreatment of the seed sludge, a high proportion of Clostridium spp. over the other bacterial species was observed at pH 5.5, and this is compatible with the high hydrogen productivity. Consequently, pH 5.5, HRT 10 h, and OLR 15 kg/m³ d were delineated as the optimal operational conditions for an ASBR fed with sugar refinery wastewater.     

Biohydrogen production from organic solid waste in a sequencing batch reactor: An optimization of the hydraulic and solids retention time

Hydrogen production from organic solids waste was evaluated using a sequencing batch reactor (SBR) under mesophilic conditions, to investigate the effect of the hydraulic retention time (HRT) and solids retention time (SRT) on hydrogen production. The examined HRT and SRT values were from 4.6 to 27 h and 17–102 h, respectively. The results showed high hydrogen production rates (1.86 LH₂/L·d) and a yield of 127.26 mLH₂/gCOD_removed for an SRT of 60 h and an HRT of 16 h. The highest chemical oxygen demand (COD) removal (38.6 ± 6.9%) was also obtained under those conditions. The highest substrate hydrolysis percentage (73.0 ± 11.4%) was obtained at an HRT of 16 h and an SRT of 102 h. A short SRT of 20 h affected hydrogen production, which decreased up to 90%. With an SRT of 20 h and an HRT of 16 h, acetic acid-like fatty acids were mainly obtained. In experiments with a long SRT (60 h), the obtained fatty acid was butyrate. The conversion efficiencies for converting particulate material into fatty acids were 51–47% using a long SRT; a short HRT resulted in percentages of 37–40%. A 3D surface analysis was performed using the maximum hydrogen yield conditions as the central point, showing that the optimal hydrogen production can be obtained with an HRT of 16 h and an SRT of 55 h. Microbial analysis showed the predominance of the Olsenella genus at an HRT< 8 h and the presence of Clostridium at an HRT of 16 h. The HRT is the main parameter leading the community composition in the process.     

Hydrogen production from alcohol distillery wastewater containing high potassium and sulfate using an anaerobic sequencing batch reactor

In this study, the feasibility of hydrogen production from alcohol distillery wastewater containing high potassium and sulfate was investigated using an anaerobic sequencing batch reactor (ASBR). The seed sludge taken from an anaerobic tank treating the distillery wastewater was boiled for 15 min before being fed to the ASBR. The ASBR system was operated under different feed chemical oxygen demand (COD) values and different COD loading rates at a mesophilic temperature of 37 °C, a controlled pH at 5.5, and a cycle time of 6 cycles per day. When the studied ASBR was operated under the best conditions (providing a maximum hydrogen production efficiency) of a feed COD of 40,000 mg/l, a COD loading rate of 60 kg/m³ d, and a hydraulic retention time of 16 h, the produced gas was found to contain 34.7% H₂ and 65.3% CO_2, without any methane being detected. Under these best conditions, the specific hydrogen production rate (SHPR) of 270 ml H₂/g MLVSS d (or 3310 ml H₂/l d), and hydrogen yield of 172 ml H₂/g COD removed, were obtained. When the feed COD exceeded 40,000 mg/l, the process performance in terms of hydrogen production decreased because of the potassium and sulfate toxicity.