Showing papers on "Hydraulic retention time published in 2017"

Simultaneous microalgae cultivation and wastewater treatment in submerged membrane photobioreactors: A review

Abstract: This review focuses on the potential advantages and challenges of submerged membrane photobioreactors (MPBRs) for microalgae cultivation and wastewater treatment. MPBR technology combines a conventional photobioreactor (PBR) with a membrane process to grow microalgae, enabling complete retention of algal biomass. Microalgae populations in MPBRs are affected by a number of factors, including wastewater characteristics and operational conditions. Although the wastewater types used in previous MPBR studies varied significantly in terms of composition, especially nitrogen (7.5 to 25 mg/L) and phosphorus (0.15 to 20 mg/L) concentrations, general trends and some optimised operating conditions can now be defined. Individual parameters, including hydraulic retention time (HRT), solids retention time (SRT), lighting, aeration, temperature, and pH were all found to be important factors affecting process efficiency; furthermore, there is evidently complex inter-relationships between these parameters, which should not be overlooked during MPBR design. Membrane fouling is still considered an operational challenge, with previous studies focusing on the relationship between membrane performances and algal organic matter. Applying immobilised microalgal technology to MPBRs has the potential to enhance productivity and mitigate fouling.

A review of biogas production from palm oil mill effluents using different configurations of bioreactors

Abstract: Palm oil mill effluent (POME) is generated from the sterilization, condensation and hydrocycloning of palm oil in mills. If the effluent is discharged into the aquatic and terrestrial ecosystem without treatment, it could lead to high biological oxygen demand (BOD), chemical oxygen demand (COD) and acidic pH of the receiving waters. Biogas consisting mostly of methane, carbon dioxide, and to a lesser hydrogen has been produced through anaerobic treatment of this toxic effluent. The process of biogas production involves microbial synthesis involving hydrolysis, acidogenesis, acetogenesis and methanogenesis. Biogas is formed during anaerobic degradation of POME by indigenous microbial communities. This review updates the current state of art of biogas production through anaerobic digestion of POME using different configurations of reactors such as fluidized bed reactor, anaerobic filtration, up-flow anaerobic sludge blanket (UASB) reactor, anaerobic contact digestion, up-flow anaerobic sludge fixed-film (UASFF) reactor, modified anaerobic baffled bioreactor (MABB), anaerobic baffled bioreactor (ABR), continuous stirred tank reactor (CSTR), expanded granular sludge bed (EGSB) reactor, Ultrasonicated membrane anaerobic system (UMAS), Ultrasonic-assisted Membrane Anaerobic System (UAMAS), membrane anaerobic system (MAS)and upflow anaerobic sludge blanket reactor (UASBR). The factors that influences biogas yield during treatment include pH, temperature (environmental factors), organic loading rate (OLR), hydraulic retention time (HRT), mixing rate, pressure, equilibrium, nutrient and microbial activities (Internal factors). Based on this study, UAMAS is the best configuration for methane production from POME during anaerobic treatment. Biogas from POME could contribute to energy sources of oil palm producing nations, while preventing the attendant environmental impacts associated with its disposal.

Continuous long-term electricity-driven bioproduction of carboxylates and isopropanol from CO2 with a mixed microbial community

Abstract: Electricity-driven bioproduction processes such as microbial electrosynthesis enable converting CO 2 and organic feedstocks into target chemicals with minimal addition of external chemicals. Bioelectrochemical CO 2 conversion to (mainly) acetate has mostly been demonstrated in batch processes. Continuous reactor operation and the operational parameters associated with it have received limited attention. Here, we demonstrate that improving bioelectrochemical reactor design to a higher cathode surface to volume ratio results in an enhanced acetate titer; 5.7 ± 0.74 g L −1 (11.5 ± 6.6 g m −2 d −1 ) in galvanostastically controlled (−5 A m −2 cathode ) batch reactors with a mixed microbial community. A long-term and stable bioproduction process could be established in which hydraulic residence time (HRT) affected the product patterns as well as the acetate production rate, up to 21 g m −2 d −1 for an HRT of 3.3d (63% coulombic efficiency) was achieved; the highest reported thus far in a continuous process. The specific energy input per kilogram of acetic acid produced during batch and continuous processes (HRT: 3.3d) was 29 ± 0.7 and 16 ± 1.3 kWh el kg −1 , respectively. Butyrate and isopropanol were the other major biochemicals produced at maximum rates of 3.7 and 3.3 g m −2 d −1 (18.6% and 21.8% of the electrons, respectively) leading to titers of 0.67 and 0.82 g L −1 during the continuous process. This is the first report on the production of a secondary alcohol (isopropanol), using a mixed culture, in CO 2 fed systems. The product ratios between these organics could be steered based on operational pH and HRTs. Operating reactors at an HRT of 5 d at pH 5 led to stable production of butyrate (1.9 ± 0.6 g m −2 d −1 ) and isopropanol (1.17 ± 0.34 g m −2 d −1 ). Cyclic voltammetry suggested an “ennoblement” of the cathode over time, shifting the onset for reductive current by more than 150 mV. Microbial community analysis revealed Acetobacterium as the main bacterial group involved in CO 2 reduction to acetate, and the presence of diverse bacterial groups in response to different operational conditions.

Complete Nitrogen Removal from Synthetic Anaerobic Sludge Digestion Liquor through Integrating Anammox and Denitrifying Anaerobic Methane Oxidation in a Membrane Biofilm Reactor

Abstract: Partial nitritation and Anammox processes are increasingly used for nitrogen removal from anaerobic sludge digestion liquor. However, their nitrogen removal efficiency is often limited due to the production of nitrate by the Anammox reaction and the sensitivity to the nitrite to ammonium ratio. This work develops and demonstrates an innovative process that achieves complete nitrogen removal from partially nitrified anaerobic sludge digestion liquor through the use of a membrane biofilm reactor (MBfR), with methane supplied through hollow fiber membranes. When steady state with a hydraulic retention time (HRT) of 1 day was reached, the process achieved complete nitrite and ammonium removal at rates of 560 mg N/L/d and 470 mg N/L/d, respectively, without any nitrate accumulation. The process is relatively insensitive to the nitrite to ammonium ratio, achieving complete nitrogen removal when their ratio in influent varied in the range of 1.125–1.32. Pyrosequencing and fluorescence in situ hybridization analy...

Optimising biogas production from anaerobic co-digestion of chicken manure and organic fraction of municipal solid waste

Abstract: In this study, it was observed that in experimental work under laboratory scale using conventional biochemical methane potential (BMP) assay, the loading rate ratio 4:1 had optimum biodegradability rate than other ratios which were investigated, while the loading rate ratio of 1:1 had optimum biogas and methane yield after 15 days hydraulic retention time It was concluded that chicken waste (CM) mono-digestion has higher biodegradability rate compare to organic fraction municipality solid waste (OFMSW) mono-digestion Co-digestion of OFMSW and CM stabilizes conditions in digestion process such as carbon to nitrogen (C:N) ratio in the substrate mixtures as well as macro and micronutrients, pH, inhibitors or toxic compounds, dry matter and thus increasing biogas production It was concluded that the organic waste generated in the municipal landfills could be co-digested with CM to produce methane which can be used as a source of environmentally friendly and clean energy for the transport sector, industries and residential homes

The effect of temperature and retention time on methane production and microbial community composition in staged anaerobic digesters fed with food waste

Abstract: Food waste is a large bio-resource that may be converted to biogas that can be used for heat and power production, or as transport fuel. We studied the anaerobic digestion of food waste in a staged digestion system consisting of separate acidogenic and methanogenic reactor vessels. Two anaerobic digestion parameters were investigated. First, we tested the effect of 55 vs. 65 °C acidogenic reactor temperature, and second, we examined the effect of reducing the hydraulic retention time (HRT) from 17 to 10 days in the methanogenic reactor. Process parameters including biogas production were monitored, and the microbial community composition was characterized by 16S amplicon sequencing. Neither organic matter removal nor methane production were significantly different for the 55 and 65 °C systems, despite the higher acetate and butyrate concentrations observed in the 65 °C acidogenic reactor. Ammonium levels in the methanogenic reactors were about 950 mg/L NH4 + when HRT was 17 days but were reduced to 550 mg/L NH4 + at 10 days HRT. Methane production increased from ~ 3600 mL/day to ~ 7800 when the HRT was decreased. Each reactor had unique environmental parameters and a correspondingly unique microbial community. In fact, the distinct values in each reactor for just two parameters, pH and ammonium concentration, recapitulate the separation seen in microbial community composition. The thermophilic and mesophilic digesters were particularly distinct from one another. The 55 °C acidogenic reactor was mainly dominated by Thermoanaerobacterium and Ruminococcus, whereas the 65 °C acidogenic reactor was initially dominated by Thermoanaerobacterium but later was overtaken by Coprothermobacter. The acidogenic reactors were lower in diversity (34–101 observed OTU0.97, 1.3–2.5 Shannon) compared to the methanogenic reactors (472–513 observed OTU0.97, 5.1–5.6 Shannon). The microbial communities in the acidogenic reactors were > 90% Firmicutes, and the Euryarchaeota were higher in relative abundance in the methanogenic reactors. The digestion systems had similar biogas production and COD removal rates, and hence differences in temperature, NH4 + concentration, and pH in the reactors resulted in distinct but similarly functioning microbial communities over this range of operating parameters. Consequently, one could reduce operational costs by lowering both the hydrolysis temperature from 65 to 55 °C and the HRT from 17 to 10 days.

Low Temperature Domestic Wastewater Treatment in a Microbial Electrolysis Cell with 1 m2 Anodes: Towards System Scale-Up†

Abstract: The potential benefits of applying microbial electrolysis cell (MEC) technology to wastewater treatment are clear and profound. Previous pilot studies have demonstrated a ‘proof of concept' with domestic waste at ambient temperatures, but have not yet treated waste to required discharge standards, and have not reached energy neutrality. In addition, these reactors have been many orders of magnitude smaller than would be needed for full scale wastewater treatment plants. Scale-up affects many of the parameters that underpin performance; understanding its impact will be vital to further progress. Modifying a previously tested cassette-style design, we reduced the internal resistance, and increased the module size by a factor of 16, constructing an MEC with six 1 m2 anodes. This created an anodic surface area to volume ratio of 34 m2 m−3. The system was operated at a hydraulic retention time of 5 hours on settled domestic wastewater for 217 days, producing more current than a scaled-down reactor, which was run in parallel. The large MEC produced 0.8 L of 93% pure H2 d−1 at ambient winter temperatures (11.4 ± 2.5 °C). Chemical oxygen demand (COD) removal averaged 63.5% with an average effluent quality of 124.7 mgCOD L−1, achieving the European Urban Wastewater Treatment Directive (1991) consent.

Biodegradation of textile dyeing industry wastewater using modified anaerobic sequential batch reactor – Start-up, parameter optimization and performance analysis

Abstract: In this study a novel modified anaerobic sequential batch reactor (MASBR) was employed to treat the textile dyeing industry wastewater. The anaerobic sequential batch reactor (ASBR) was modified by the addition of a sorbent (ground nut shell powder) and plastic media. The start-up phase of the MASBR was observed over a period of 80 days. Statistical based experiments were performed in order to optimize the parameters viz., sorbent dosage and particle loading, and to study the interactive effects using response surface method (RSM). At the optimized conditions, experiments were performed at various organic loading rates by varying initial textile dye wastewater concentration and hydraulic retention time (HRT). The anaerobic biodegradation of textile dyeing wastewater in the MASBR was analyzed in terms of decolorization, COD reduction, biogas production, volatile fatty acids (VFA) at different organic loading rate (OLR) between 0.110 and 0.650 kgCOD/m3 d. A maximum decolorization of 94.8% and COD reduction of 97.1% were obtained in the MASBR. The novel sorbent utilized in the study was characterized using FTIR and SEM analysis.

Removal of Pharmaceuticals from Wastewater by Intermittent Electrocoagulation

Abstract: The continuous release of emerging contaminants (ECs) in the aquatic environment, as a result of the inadequate removal by conventional treatment methods, has prompted research to explore viable solutions to this rising global problem. One promising alternative is the use of electrochemical processes since they represent a simple and highly efficient technology with less footprint. In this paper, the feasibility of treating ECs (i.e., pharmaceuticals) using an intermittent electrocoagulation process, a known electrochemical technology, has been investigated. Diclofenac (DCF), carbamazepine (CBZ) and amoxicillin (AMX) were chosen as being representative of highly consumed drugs that are frequently detected in our water resources and were added in synthetic municipal wastewater. The removal efficiencies of both individual and combined pharmaceuticals were determined under different experimental conditions: hydraulic retention time (HRT) (6, 19 and 38 h), initial concentration (0.01, 4 and 10 mg/L) and intermittent application (5 min ON/20 min OFF) of current density (0.5, 1.15 and 1.8 mA/cm2). Results have shown that these parameters have significant effects on pharmaceutical degradation. Maximum removals (DCF = 90%, CBZ = 70% and AMX = 77%) were obtained at a current density of 0.5 mA/cm2, an initial concentration of 10 mg/L and HRT of 38 h.

Effect of Hydraulic Retention Time on Anaerobic Digestion of Wheat Straw in the Semicontinuous Continuous Stirred-Tank Reactors.

Abstract: Three semicontinuous continuous stirred-tank reactors (CSTR) operating at mesophilic conditions (35°C) were used to investigate the effect of hydraulic retention time (HRT) on anaerobic digestion of wheat straw. The results showed that the average biogas production with HRT of 20, 40, and 60 days was 46.8, 79.9, and 89.1 mL/g total solid as well as 55.2, 94.3, and 105.2 mL/g volatile solids, respectively. The methane content with HRT of 20 days, from 14.2% to 28.5%, was the lowest among the three reactors. The pH values with HRT of 40 and 60 days were in the acceptable range compared to that with HRT of 20 days. The propionate was dominant in the reactor with HRT of 20 days, inhibiting the activities of methanogens and causing the lower methane content in biogas. The degradation of cellulose, hemicellulose, and crystalline cellulose based on XRD was also strongly influenced by HRTs.