Two-stage Biological Process Research Articles

Optimum operational conditions for mixotrophic microalgae growth and nutrient recovery

Microalgae have been presented as microorganisms with great potential to recover nutrient from wastewater. Mixotrophic cultivation of microalgae in nutrient rich wastewater can help eliminating the deficiencies of both phototrophic and heterotrophic growth by allowing the independent optimisation of respiration and photosynthesis processes. Nutrient control and uptake by mixotrophic microalgae can be achieved either in a single or two-stage process using sequential reactors in a continuous flow system. Therefore, this work aims at studying mixotrophic microalgae growth in a two-stage biological process under continuous flow conditions with biomass recycle to recover nutrients from wastewater, considering the effects of different operational conditions (hydraulic retention time (HRT), cell retention time (CRT) and different nitrogen sources). The optimum operational conditions for algal nutrient uptake were identified to be 48 h HRT and 14 d CRT, using a mix of nitrogen sources (Ammonium-N to Nitrate-N ratio of 1:1) with 40.0% and 93.2% of phosphorus of nitrogen recovery in algal biomass, respectively.

Treatment of NSAPs-rich petrochemical wastewaters using a two-stage combined process of fungi and activated sludge

ABSTRACT A two-stage biological process using fungi and bacteria was set-up and tested for treating a petrochemical wastewater containing naphthalene sulphonic acid polymers. The fungal treatment was carried out through a trickling filter inoculated with Pleurotus ostreatus attached on Luffa cylindrica acting as both physical support and carbon source. The fungal reactor was operated in non-sterile conditions setting two pH values (5 and 6) and two hydraulic retention times (2 d and 3 d). The effluent was then sent to an activated sludge reactor operating the second stage of the treatment. Using an HPLC-based technique, it was observed that the fungal reactor was capable of reducing the polymerization grade of naphthalene sulphonic acid polymers up to 35%, thus increasing significantly the biodegradability of the petrochemical wastewater, from the initial 9% to 46%. The two-stage process allowed to remove about 50% of the total COD much higher than 9% that can be achieved with activated sludge alone. The use of Luffa cylindrica as support for fungi allowed to limit bacterial contamination of the trickling filter and enhanced enzymatic production (on average 20 U/L of Laccase) without any release of non-biodegradable by-products in the effluent. Extraction and PCR-amplification of fungal DNA was carried out along with over 70 d running process in order to monitor the changes of the fungal community inside the reactors. Results showed that Meyerozyma, Fusarium and Thricoderma, spp. developed inside the reactor with Thricoderma, spp. representing the main constituent of fungal biomass at the end of the experiment.

A two-stage biological gas to liquid transfer process to convert carbon dioxide into bioplastic

The fermentation of carbon dioxide (CO2) with hydrogen (H2) uses available low-cost gases to synthesis acetic acid. Here, we present a two-stage biological process that allows the gas to liquid transfer (Bio-GTL) of CO2 into the biopolymer polyhydroxybutyrate (PHB). Using the same medium in both stages, first, acetic acid is produced (3.2gL−1) by Acetobacterium woodii from 5.2L gas-mixture of CO2:H2 (15:85v/v) under elevated pressure (≥2.0bar) to increase H2-solubility in water. Second, acetic acid is converted to PHB (3gL−1 acetate into 0.5gL−1 PHB) by Ralstonia eutropha H16. The efficiencies and space-time yields were evaluated, and our data show the conversion of CO2 into PHB with a 33.3% microbial cell content (percentage of the ratio of PHB concentration to cell concentration) after 217h. Collectively, our results provide a resourceful platform for future optimization and commercialization of a Bio-GTL for PHB production.

A novel anoxic-aerobic biofilter process using new composite packing material for the treatment of rural domestic wastewater.

A pilot scale experiment was conducted to evaluate the characteristics of contaminants removal in a continuously two-stage biological process composed of an anoxic biofilter (AF) and an biological aerated filter (BAF). This novel process was developed by introducing new composite packing material (MZF) into bioreactors to treat rural domestic wastewater. A comparative study conducted by the same process with ceramsite as packing material under the same conditions showed that a MZF system with a Fe proportion in the packing material performed better in chemical oxygen demand (COD) removal (average 91.5%), ammonia (NH4(+)-N) removal (average 98.3%), total nitrogen (TN) removal (average 64.8%) and total phosphorus (TP) removal (average 90%). After treatment of the MZF system, the concentrations of COD, NH4(+)-N, TN and TP in effluent were 20.3 mg/L, 0.5 mg/L, 11.5 mg/L and 0.3 mg/L, respectively. The simultaneously high efficiencies of nitrification, denitrification and phosphorus removal were achieved by the coupling effects of biological and chemical processes in the MZF system. The results of this study showed that the application of MZF might be a favorable choice as packing material in biofilters for treatment of rural domestic wastewater.

Simultaneous Dephenolization and Decolorization of Treated Palm Oil Mill Effluent by Oil Palm Fiber-Immobilized Trametes Hirsuta Strain AK 04

The phenolics and high organic content present in palm oil mill effluent are the major contributors to its dark brown color, toxicity, and antimicrobial properties. In this study, ten white rot fungi were screened for their potential in the dephenolization and decolorization of treated palm oil mill effluent (TPOME) in solid and liquid state cultures. Among them, Trametes hirsuta strain AK 04 was found to be more tolerant to high TPOME concentrations and showed the highest phenolics and color removal activities. This strain was immobilized onto oil palm fibers (OPFs) and appeared more resistant to inhibitory compounds such as phenolics in TPOME than the free cell culture. The OPF-immobilized fungus was able to effectively remove phenolics and color of TPOME without effluent dilution and addition of nutrients. The activities of laccase and manganese peroxidase were found during dephenolization and decolorization processes. Moreover, the degradation rate of immobilized fungus could be accelerated by pretreatment of phenolics with phenol-degrading bacteria. This method improved the fungal dephenolization and decolorization simultaneously up to 82.2 ± 3.8 % and 87.1 ± 1.1 % after 8 days of incubation. Therefore, a two-stage biological process containing phenol-degrading bacteria and OPF-immobilized fungus could be a feasible and economical method for simultaneous improvement of dephenolization and decolorization of TPOME.

Analysis of the bacterial community in a full-scale printing and dyeing wastewater treatment system based on T-RFLP and 454 pyrosequencing

In this study, the bacterial dynamics and structure compositions in the two-stage biological process of a full-scale printing and dyeing wastewater (PDW) treatment system were traced and analyzed by terminal restriction fragment length polymorphism (T-RFLP) and 454 pyrosequencing techniques. T-RFLP analysis showed that the microbial communities experienced significant variation in the process of seed sludge adaptation to the PDW environments and were in constant evolution during the whole running period of the system, despite the constant COD and color removal effects. Pyrosequencing results indicated that the two-stage biological system harbored rather diverse bacteria, with Proteobacteria being the predominant phylum during the steady running period, although its microbial compositions differed. The first-stage aerobic tank was dominated by α-Proteobacteria (89.05% of Proteobacteria), whereas in the second-stage aerobic tank, β- and γ-Proteobacteria, besides α-Proteobacteria, were the dominant bacterial populations.

Long-term study of nitrate, nitrite and pesticide removal from groundwater: A two-stage biological process

The simultaneous biological removal of nitrate, atrazine, deethylatrazine and metolachlor, chemicals frequently encountered in groundwater, in a two-stage continuous system, was studied. A primary denitrification step in a reactor packed with ceramic biofilm carrier was followed by passage through an aerobic expanded-bed reactor packed with Kaldnes™ carrier. This second step removes almost all NO2–N and up to 78% total organic carbon (TOC) residues passed by the denitrifying reactor. In spite of shock loads and other environmental changes, the two-stage process removes more than 99% of nitrate at the rate of 0.34 g l−1 NO3–N day, and up to 80% of deethylatrazine, 25% of atrazine, and 45% of metolachlor. However, the final effluent exceeded the maximum contaminant levels for pesticides and total organic carbon according to the EU Drinking Water Directive.

The effect of dilution and l-malic acid addition on bio-hydrogen production with Rhodopseudomonas palustris from effluent of an acidogenic anaerobic reactor

In this study, H 2 was produced from cheese whey wastewater in a two-stage biological process: i) first stage; thermophilic dark fermentation ii) second stage; the photo fermentation using Rhodopseudomonas palustris strain DSM 127 ( R. palustris). The effect of both dilution and addition of l-malic acid on the hydrogen production was investigated. Among the dilution rates used, 1/5 dilution ratio was found to produce the best hydrogen production (349 ml H 2/g COD fed). On the other hand, It was seen that the mixing the effluent with l-malic acid at increasing ratios had further positive effect and improved the hydrogen production significantly. It was concluded that dilution of the feeding helps to reduce the nitrogen content and the volatile fatty acid content that might be otherwise harmful to the photo-heterotrophic organisms. Overall hydrogen production yield (for dark + photo fermentation) was found to vary 2 and 10 mol H 2/mol lactose. Second conclusion is that cheese whey effluent should be mixed with a co-substrate containing l-malic acid such as apple juice processing effluents before fed into the photo fermentation reactor.

A two-stage, two-organism process for biohydrogen from glucose

H 2 can potentially be produced in a two-stage biological process: the fermentation of glucose by Escherichia coli HD701 and the photofermentation of the residual medium by Rhodobacter sphaeroides O.U. 001. In a typical batch fermentation, E. coli consumed glucose and produced H 2 , organic end-products and biomass. Organic end-products and residual glucose were removed during subsequent photofermentation by R. sphaeroides, with associated growth and neutralization of pH. However, photoproduction of H 2 did not occur during photofermentation of the residual liquor per se due to the presence of fixed nitrogen compounds. Nevertheless, this two-stage approach could be applied to dispose of sugar-containing industrial wastes, H 2 being used for on-site power generation.

２段生物処理法およびオゾン処理による皮革工場廃水混入下水からＣＯＤと色度の削減

Industrial wastewaters containing high concentrations of organic substances and ammonia nitrogen, such as leather industry wastewater, are sometimes treated by an activated sludge process in a sewage treatment plant. Such wastewaters tend to raise COD and color in the effluent of an activated sludge process. Refractory organic substance and nitrite build-up are the main causes of COD. It is difficult to reduce COD and color efficiently by the conventional activated sludge process.We studied a two-stage biological process combined an activated sludge process and a fixed-bed reactor to treat leather industry wastewater efficiently. And the use of ozone was studied to reduce COD and color.A two-stage biological process could promote nitrification reaction producing nitrate. COD originated from nitrite build-up was not observed. However, the two-stage biological process could not remove color.Ozone could reduce both COD and color in the effluent of an activated sludge process. However, nitrite build-up worsened the efficiency of ozone oxidation. In view of the economical point, it is important to prevent nitrite build-up in a biological process.