The enzymatic reduction of Cr(VI) to Cr(III) by Cr(VI) resistant bacteria followed by chemical precipitation constitutes the ChromeBac system. Acinetobacter haemolyticus was immobilized onto carrier material inside a 0.2m(3) bioreactor. Neutralized electroplating wastewater with Cr(VI) concentration of 17-81 mg L(-1) was fed into the bioreactor (0.11-0.33 m(3)h(-1)). Complete Cr(VI) reduction to Cr(III) was obtained immediately after the start of bioreactor operation. Together with the flocculation, coagulation and filtration, outflow concentration of less than 0.02 mg Cr(VI)L(-1) and 1mg total CrL(-1) were always obtained. Performance of the bioreactor was not affected by fluctuations in pH (6.2-8.4), Cr(VI) (17-81 mg L(-1)), nutrient (liquid pineapple waste, 1-20%v/v) and temperature (30-38 degrees C). Standby periods of up to 10 days can be tolerated without loss in activity. A robust yet effective biotechnology to remove chromium from wastewater is thus demonstrated.
Palm oil mill effluent (POME) is a highly polluting wastewater that pollutes the environment if discharged directly due to its high chemical oxygen demand (COD) and biochemical oxygen demand (BOD) concentration. Anaerobic digestion has been widely used for POME treatment with large emphasis placed on capturing the methane gas released as a product of this biodegradation treatment method. The anaerobic digestion method is recognized as a clean development mechanism (CDM) under the Kyoto protocol. Certified emission reduction (CER) can be obtained by using methane gas as a renewable energy. This review aims to discuss the various anaerobic treatments of POME and factors that influence the operation of anaerobic treatment. The POME treatment at both mesophilic and thermophilic temperature ranges are also analyzed.
A sequential optimization based on statistical design and one-factor-at-a-time (OFAT) method was employed to optimize the media constituents for the improvement of citric acid production from oil palm empty fruit bunches (EFB) through solid state bioconversion using Aspergillus niger IBO-103MNB. The results obtained from the Plackett-Burman design indicated that the co-substrate (sucrose), stimulator (methanol) and minerals (Zn, Cu, Mn and Mg) were found to be the major factors for further optimization. Based on the OFAT method, the selected medium constituents and inoculum concentration were optimized by the central composite design (CCD) under the response surface methodology (RSM). The statistical analysis showed that the optimum media containing 6.4% (w/w) of sucrose, 9% (v/w) of minerals and 15.5% (v/w) of inoculum gave the maximum production of citric acid (337.94 g/kg of dry EFB). The analysis showed that sucrose (p<0.0011) and mineral solution (p<0.0061) were more significant compared to inoculum concentration (p<0.0127) for the citric acid production.
Moving bed sequencing batch reactors (MBSBRs) packed with 8% (v/v) of 8-, 27- and 64-mL polyurethane (PU) foam cubes, respectively, were investigated for simultaneous 4-chlorophenol (4-CP) and nitrogen removal at increasing 4-CP concentration. When the 4-CP concentration exceeded 300 mg L(-1), the MBSBR with 27-mL foam cubes was observed to outperform the other MBSBRs in removing 4-CP and nitrogen. The reasons were: (1) there were more biomass in inner layer of the 27-mL cubes, compared to that of the 8-mL cubes, which was more shielded from the inhibitory effect of 4-CP and (2) the 27-mL cubes were more mobile than the 64-mL cubes. Although increasing 4-CP concentration to 600 mg L(-1) resulted in incomplete removal of 4-CP in the MBSBRs, results of the batch reactor with 27-mL foam cubes showed that complete 4-CP removal within the REACT period could be achieved by increasing the packing volume to 20%.
Illumination factors such as length of photoperiod and intensity can affect growth of microalgae and lipid content. In order to optimize microalgal growth in mass culture system and lipid content, the effects of light intensity and photoperiod cycle on the growth of the marine microalgae, Nannochloropsis sp. were studied in batch culture. Nannochloropsis sp. was grown aseptically for 9 days at three different light intensities (50, 100 and 200 μmol m(-2) s(-1)) and three different photoperiod cycles (24:0, 18:06 and 12:12 h light:dark) at 23 °C cultivation temperature. Under the light intensity of 100 μmol m(-2) s(-1) and photoperiod of 18 h light: 6 h dark cycle, Nannochloropsis sp. was found to grow favorably with a maximum cell concentration of 6.5×10(7) cells mL(-1), which corresponds to the growth rate of 0.339 d(-1) after 8 day cultivation and the lipid content was found to be 31.3%.
The physical factors affecting the production of an organic solvent-tolerant protease from Pseudomonas aeruginosa strain K was investigated. Growth and protease production were detected from 37 to 45 degrees C with 37 degrees C being the optimum temperature for P. aeruginosa. Maximum enzyme activity was achieved at static conditions with 4.0% (v/v) inoculum. Shifting the culture from stationary to shaking condition decreased the protease production (6.0-10.0% v/v). Extracellular organic solvent-tolerant protease was detected over a broad pH range from 6.0 to 9.0. However, the highest yield of protease was observed at pH 7.0. Neutral media increased the protease production compared to acidic or alkaline media.
The present study demonstrated that aerobic granular sludge is capable of treating livestock wastewater from a cattle farm in a sequencing batch reactor (SBR) without the presence of support material. A lab scale SBR was operated for 80 d using 4 h cycle time with an organic loading rate (OLR) of 9 kg COD m(-3) d(-1). Results showed that the aerobic granules were growing from 0.1 to 4.1 mm towards the end of the experimental period. The sludge volume index (SVI) was 42 ml g(-1) while the biomass concentration in the reactor grew up to 10.3 g L(-1) represent excellent biomass separation and good settling ability of the granules. During this period, maximum COD, TN and TP removal efficiencies (74%, 73% and 70%, respectively) were observed in the SBR system, confirming high microbial activity in the SBR system.
The effects of Mecoprop (RS)-MCPP were investigated in an anaerobic membrane bioreactor (AnMBr) fed with synthetic wastewater containing stepwise increases in Mecoprop concentration, 5-200 mg L(-1) over 240 days. Effects were observed in terms of soluble chemical oxygen demand (COD) removal efficiency, volatile fatty acid (VFA) production, and methane yield. Soluble COD removal efficiency was stable at Mecoprop concentrations below 200 (±3) mg L(-1), with an average of 98 (±0.7)% removal. However, at 200 (±3) mg L(-1) Mecoprop, the COD removal efficiency decreased gradually to 94 (±1.5)%. At 5 mg L(-1) Mecoprop, acetic and propionic acid concentrations increased by 60% and 160%, respectively. In contrast, when Mecoprop was increased to 200 (±3) mg L(-1), the formation and degradation of acetate was unaffected by the higher Mecoprop concentration, acetate remaining below 35 mg L(-1). Increases in the Mecoprop specific utilization rate were observed as Mecoprop was increased stepwise between 5 and 200 mg L(-1).
Aerobic granular sludge (AGS) was successfully cultivated at 27±1 °C and pH 7.0±1 during the treatment of rubber wastewater using a sequential batch reactor system mode with complete cycle time of 3 h. Results showed aerobic granular sludge had an excellent settling ability and exhibited exceptional performance in the organics and nutrients removal from rubber wastewater. Regular, dense and fast settling granule (average diameter, 1.5 mm; settling velocity, 33 m h(-1); and sludge volume index, 22.3 mL g(-1)) were developed in a single reactor. In addition, 96.5% COD removal efficiency was observed in the system at the end of the granulation period, while its ammonia and total nitrogen removal efficiencies were up to 94.7% and 89.4%, respectively. The study demonstrated the capabilities of AGS development in a single, high and slender column type-bioreactor for the treatment of rubber wastewater.
Palm kernel cake (PKC), an agro-industrial by-product used extensively in the animal feed industry, has limited use in fish feeds due to its high fiber and low protein contents. In this study, PKC was processed under solid state culture conditions with five fungal strains and the effect of this fungal culturing on the amino acid, fatty acid, cellulose and hemicellulose fractions was evaluated. Fungal strains used were Sclerotium rolfsii, Trichoderma harzianum, Trichoderma longiobrachiatum, Trichoderma koninggi and Aspergillus niger. Fungal growth was carried out at 50% moisture level and 1% inoculum level for 7 days. A significant increase in protein content from 18.76% to 32.79% was obtained by growing T. longibrachiatum on PKC. Cellulose level decreased significantly from 28.31% to 12.11% for PKC cultured with T. longibrachiatum, and hemicellulose from 37.03% to 19.01% for PKC cultured with A. niger. Fungal culturing of PKC brought about an increase in the level of unsaturated- and a decrease in the level of the saturated-fatty acids.
Polyhydroxyalkanoate (PHA) recovery from aerobic granules was investigated using four cell digestion agents, namely, sodium hypochlorite, sodium hydroxide, acetone and sodium chloride. Simultaneously, the removal of extracellular polymeric substances (EPS) and its effect on PHA yield were investigated. The highest PHA recovery yield was obtained using sodium hypochlorite, accounting for 89% cell dry weight (CDW). The highest PHA was recovered after the sodium hypochlorite completely removed the EPS from the aerobic granules. The average molecular weight (Mw) of the PHA recovered using sodium hypochlorite was 5.31 × 10(5)g/mol with only 1.8% molecular weight degradation. The energy and duration analysis for PHA recovery revealed that the sodium hypochlorite method required the least amount of energy and time at 0.0561 MJ/g PHA and 26 h, respectively. The PHA that was recovered was a P3(HB-co-HV) co-polymer.
The influence of TiO2 nanoparticles (TiO2-NPs) (10-50mg/L) on aerobic granulation of algal-bacterial symbiosis system was investigated by using two identical sequencing batch reactors (SBRs). Although little adverse effect was observed on their nitritation efficiency (98-100% in both reactors), algal-bacterial granules in the control SBR (Rc) gradually lost stability mainly brought about by algae growth. TiO2-NPs addition to RT was found to enhance the granulation process achieving stable and compact algal-bacterial granules with remarkably improved nitratation thus little nitrite accumulation in RT when influent TiO2-NPs⩾30mg/L. Despite almost similar organics and phosphorus removals obtained in both reactors, the stably high nitratation efficiency in addition to much stable granular structure in RT suggests that TiO2-NPs addition might be a promising remedy for the long-term operation of algal-bacterial granular system, most probably attributable to the stimulated excretion of extracellular polymeric substances and less filamentous TM7.
The performance of a compost biofilter inoculated with mixed microbial consortium was optimized for treating a gas-phase mixture of benzene and toluene. The biofilter was acclimated to these VOCs for a period of ∼18d. The effects of concentration and flow rate on the removal efficiency (RE) and elimination capacity (EC) were investigated by varying the inlet concentration of benzene (0.12-0.95g/m(3)), toluene (0.14-1.48g/m(3)) and gas-flow rate (0.024-0.072m(3)/h). At comparable loading rates, benzene removal in the mixture was reduced in the range of 6.6-41% in comparison with the individual benzene degradation. Toluene removal in mixture was even more affected as observed from the reductions in REs, ranging from 18.4% to 76%. The results were statistically interpreted by performing an analysis of variance (ANOVA) to elucidate the main and interaction effects.
This study focuses on the evaluation of the performance of Chlorella sp. in removing nutrient in aquaculture wastewater and its correlation with the kinetic growth of Chlorella sp. The treatment was applied with various Chlorella sp. inoculation dosage ranging from 0% to 60% (v/v) of wastewater. The optimum inoculation dosage was recorded at 30% (v/v) with effluent concentration of ammonia and orthophosphate recording at 0.012mgL(-1) and 0.647mgL(-1), respectively on Day 11. The optimum dosage for bio-flocculation process was obtained at 30mgL(-1) of Aspergillus niger with a harvesting efficiency of 97%. This type of development of phytoremediation with continuous bio-harvesting could promote the use of sustainable green technology for effective wastewater treatment.
Biological removal of carbon, nitrogen and sulfur is drawing increasing research interest in search for an efficient and cost-effective wastewater treatment. While extensive work on separate removal of nitrogen and sulfur is well documented, investigation on simultaneous denitrifying sulfide removal has only been reported recently. Most of the work on denitrifying sulfide removal has been focusing on bioreactor performance, loading and operating conditions. Nonetheless, underlying principles elucidating the biochemical reactions and the mechanisms of the microbial degradation are yet to be established. In addition, unstable denitrifying sulfide removal which is a major operating problem that hinders practical application of the process, is yet to be resolved. This paper provides a review on the state-of-the-art development of simultaneous biological removal of sulfur, nitrogen and carbon. Research on bioreactor operation and performance, reactor configurations, mechanisms and modeling work including the use of mass balance analysis and artificial neural networks is delineated. An in-depth discussion on the microbial community and functional consortium is also provided. Challenges and future work on simultaneous biological removal of nitrogen-sulfur-carbon are also outlined.
The aim of this study was obtain a model that maximizes growth and production of inulinase and invertase by Aspergillus niger ATCC 20611, employing response surface methodology (RSM). The RSM with a five-variable and three-level central composite design (CCD) was employed to optimize the medium composition. Results showed that the experimental data could be appropriately fitted into a second-order polynomial model with a coefficient of determination (R2) more than 0.90 for all responses. This model adequately explained the data variation and represented the actual relationships between the parameters and responses. The pH and temperature value of the cultivation medium were the most significant variables and the effects of inoculum size and agitation speed were slightly lower. The intra-extracellular inulinase, invertase production and biomass content increased 10-32 fold in the optimized medium condition (pH 6.5, temperature 30°C, 6% (v/v), inoculum size and 150rpm agitation speed) by RSM compared with medium optimized through the one-factor-at-a-time method. The process development and intensification for simultaneous production of intra-extracellular inulinase (exo and endo inulinase) and invertase from A. niger could be used for industrial applications.
Sulfide inhibition to nitrifying bacteria has prevented the integration of digestate nitrification and biogas desulfurization to simplify anaerobic digestion systems. In this study, liquid digestate with NaHS solution was treated using nitrifying sludge in a sequential-batch reactor with a long fill period, with an ammonium loading rate of 293 mg-N L-1 d-1 and a stepwise increase in the sulfide loading rate from 0 to 32, 64, 128, and 256 mg-S L-1 d-1. Batch bioassays and microbial community analysis were also conducted with reactor sludge under each sulfide loading rate to quantify the microbial acclimatization to sulfide. In the reactor, sulfide was completely removed. Complete nitrification was maintained up to a sulfide load of 128 mg-S L-1 d-1, which is higher than that in previous reports and sufficient for biogas treatment. In the batch bioassays, the sulfide tolerance of NH4+ oxidizing activity (the 50% inhibitory sulfide concentration) increased fourfold over time with the compositional shift of nitrifying bacteria to Nitrosomonas nitrosa and Nitrobacter spp. However, the sulfur removal rate of the sludge slightly decreased, although the abundance of the sulfur-oxidizing bacteria Hyphomicrobium increased by 30%. Therefore, nitrifying sludge was probably acclimatized to sulfide not by the increasing sulfide removal rate but rather by the increasing nitrifying bacteria, which have high sulfide tolerance. Successful simultaneous nitrification and desulfurization were achieved using a sequential-batch reactor with a long fill period, which was effective in facilitating the present acclimatization.
Agro-industrial biorefinery effluent (AIBW) is considered a highly polluting source responsible for environmental contamination. It contains high loads of chemical oxygen demand (COD), and phenol, with several other organic and inorganic constituents. Thus, an economic treatment approach is required for the sustainable discharge of the effluent. The long-term process performance, contaminant removal and microbial response of AIBW to rice straw-based biochar (RSB) and biochar-based geopolymer nanocomposite (BGC) as biosorbents in an activated sludge process were investigated. The adsorbents operated in an extended aeration system with a varied hydraulic retention time of between 0.5 and 1.5 d and an AIBW concentration of 40-100% for COD and phenol removal under standard conditions. Response surface methodology was utilised to optimize the process variables of the bioreactor system. Process results indicated a significant reduction of COD (79.51%, 98.01%) and phenol (61.94%, 74.44%) for BEAS and GEAS bioreactors respectively, at 1 d HRT and AIBW of 70%. Kinetic model analysis indicated that the Stover-Kincannon model best describes the system functionality, while the Grau model was better in predicting substrate removal rate and both with a precision of between R2 (0.9008-0.9988). Microbial communities examined indicated the abundance of genera, following the biosorbent addition, while RSB and BGC had no negative effect on the bioreactor's performance and bacterial community structure of biomass. Proteobacteria and Bacteroidetes were abundant in BEAS. While the GEAS achieved higher COD and phenol removal due to high Nitrosomonas, Nitrospira, Comamonas, Methanomethylovorans and Acinetobacter abundance in the activated sludge. Thus, this study demonstrated that the combination of biosorption and activated sludge processes could be promising, highly efficient, and most economical for AIBW treatment, without jeopardising the elimination of pollutants or the development of microbial communities.
Although algal-based membrane bioreactors (AMBRs) have been demonstrated to be effective in treating wastewater (landfill leachate), there needs to be more research into the effectiveness of these systems. This study aims to determine whether AMBR is effective in treating landfill leachate with hydraulic retention times (HRTs) of 8, 12, 14, 16, 21, and 24 h to maximize AMBR's energy efficiency, microalgal biomass production, and removal efficiency using artificial neural network (ANN) models. Experimental results and simulations indicate that biomass production in bioreactors depends heavily on HRT. A decrease in HRT increases algal (Chlorella vulgaris) biomass productivity. Results also showed that 80% of chemical oxygen demand (COD) was removed from algal biomass by bioreactors. To determine the most efficient way to process the features as mentioned above, nondominated sorting genetic algorithm II (NSGA-II) techniques were applied. A mesophilic, suspended-thermophilic, and attached-thermophilic organic loading rate (OLR) of 1.28, 1.06, and 2 kg/m3/day was obtained for each method. Compared to suspended-thermophilic growth (3.43 kg/m3.day) and mesophilic growth (1.28 kg/m3.day), attached-thermophilic growth has a critical loading rate of 10.5 kg/m3.day. An energy audit and an assessment of the system's auto-thermality were performed at the end of the calculation using the Monod equation for biomass production rate (Y) and bacteria death constant (Kd). According to the results, a high removal level of COD (at least 4000 mg COD/liter) leads to auto-thermality.
Recycled paper mill effluent (RPME) contains high levels of organic and solid compounds, causing operational problems for anaerobic biological treatment. In this study, a unique modified anaerobic inclining-baffled reactor (MAI-BR) has been developed to treat RPME at various initial chemical oxygen demand (COD) concentrations (1000-4000 mg/L) and hydraulic retention times (HRTs) (3 and 1 day). The COD removal efficiency was decreased from 96 to 83% when the organic loading rate (OLR) was increased from 0.33 to 4 g/L day. Throughout the study, a maximum methane yield of 0.25 L CH4/g COD was obtained, while the pH fluctuated in the range of 5.8 to 7.8. The reactor performance was influenced by the development and distribution of the microbial communities. Based on the next-generation sequencing (NGS) analysis, the microbial community represented a variety of bacterial phyla with significant homology to Euryarchaeota (43.06%), Planctomycetes (24.68%), Proteobacteria (21.58%), Acidobacteria (4.12%), Chloroflexi (3.14%), Firmicutes (1.12%), Bacteroidetes (1.02%), and others (1.28%). The NGS analysis showed that the microbial community was dominated by Methanosaeta concilii and Candidatus Kuenenia stuttgartiensis. This can be supported by the presence of filamentous and spherical microbes of different sizes. Additionally, methanogenic and anaerobic ammonium oxidation (ANAMMOX) microorganisms coexisted in all compartments, and these contributed to the overall degradation of substances in the RPME. Graphical abstract ᅟ.