Effects of dilution and pretreatment on nutrient removal and biomass production of Chlorella vulgaris in kitchen wastewater.

This research investigated the effect of kitchen wastewater (KWW) concentrations and pretreatment methods on Chlorella vulgaris biomass production, lipid content and nutrient removal. This study was divided into two separate experiments. The first experiment determined the appropriate dilution rate of KWW for the growth of microalgae, sterilized KWW was varied between 25%, 50%, 75%, and 100%(v/v). The result indicated that 50%(v/v) showed the highest nutrient removal by 90.23%, 85.87%, and 80.64% of sCOD, TKN, and TP, respectively. The highest biomass and lipid content were obtained with 50%(v/v) (1.447 g/L, 37.9%). The second experiment was to find an effective physical pretreatment method, which separated the biotic contaminant, non-sterilized KWW was diluted 50%(v/v) and filtered with different mesh size filters (150 µm, 50 µm, and 30 µm) compared with sterilized KWW as a control sample. The result indicated that pretreatment with 50 µm filtration was found highest nutrient removal by 90.51%, 84.74%, and 77.50% of sCOD, TKN, and TP, respectively. The highest biomass and lipid content were obtained with 50 µm filtration (1.496 g/L, 39.4%). Our results support the hypothesis that the optimal dilution and proper filtration of KWW helps create more favorable environment for microalgal growth.

The application of microalgae in actual wastewater treatment was the improper amount of nutrients and the presence of biotic contaminant in the non-sterilized wastewater, which is inhibit the microalgae growth. Hence, it is necessary to develop the technique for controlling biotic contamination and appropriately diluting wastewater to enable full-scale microalgae cultivation in the future.

Effects of high-strength landfill leachate effluent on stress-induced microalgae lipid production and post-treatment micropollutant degradation.

This research investigates the effects of landfill leachate effluent concentrations from moving bed biofilm reactor (MBBR) on stress-induced Chlorella vulgaris and Scenedesmus armatus lipid production and post-treatment micropollutant degradation. The effluent concentrations were varied between 25%, 50%, 75%, and 100% (v/v). The landfill leachate influent was treated using two-stage moving bed biofilm reactor under 24 h and 18 h hydraulic retention time (HRT). The results indicated that the effluent concentration was positively correlated with the stress-induced microalgae lipid production in the post-treatment of residual micropollutants. C. vulgaris and S. armatus completely remove residual micropollutants in the effluent. The superoxide dismutase and peroxidase activity were positively correlated with the cellular lipid content. The lipid content of C. vulgaris and S. armatus cultivated in the 18 h HRT effluent were 31-51% and 51-64%, while those in the 24 h HRT effluent were 15-16% and 5-19%. The optimal condition of microalgae cultivation for the post-treatment of residual micropollutants was 50-75% (v/v) effluent concentrations under 18 h HRT, achieving the highest lipid production of 113-116 mg/L for C. vulgaris and 74-75 mg/L for S. armatus. Essentially, the MBBR landfill leachate effluent holds promising potential as a substrate for microalgae lipid production.

Treatment efficiency and greenhouse gas emissions of non-floating and floating bed activated sludge system with acclimatized sludge treating landfill leachate.

This research investigates the treatment efficiency and greenhouse gas (GHG) emissions of non-floating and floating bed AS systems with acclimatized sludge treating landfill leachate. The GHGs under study included carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The non-floating and floating bed AS systems were operated in parallel with identical landfill leachate influent under different hydraulic retention time (HRT) conditions (24, 18, and 12 h). The experimental results showed that the treatment efficiency of organic compounds under 24 h HRT of both systems (90 - 98%) were insignificantly different, while the nutrient removal efficiency of both systems were between 54 and 98 %. The treatment efficiency of the floating bed AS system, despite shorter HRT, remained relatively unchanged due to an abundance of effective bacteria residing in the floating media. The CO2 emissions were insignificantly different between both AS systems under all HRT conditions (22 - 26.3 µmol/cm2.min). The CO2 emissions were positively correlated with organic loading but inversely correlated with HRT. The CH4 emissions were positively correlated with HRT (26.3 µmol/cm2.min under 24 h HRT of the floating bed AS system). The N2O emissions were positively correlated with nitrogen loading, and the N2O emissions from the floating bed AS system were lower due to an abundance of N2O-reducing bacteria. The floating media enhanced the biological treatment efficiency while maintaining the bacterial community in the system. However, the floating media promoted CH4 production under anoxic conditions. The originality of this research lies in the use of floating media in the biological treatment system to mitigate GHG emissions, unlike existing research which focused primarily on enhancement of the treatment efficiency.

Use of aged sludge bioaugmentation in two-stage activated sludge system to enhance the biodegradation of toxic organic compounds in high strength wastewater.

This research investigates the toxic organic compounds biodegradation efficiency of two-stage activated sludge systems with (bioaugmented) and without aged sludge bioaugmentation (non-bioaugmented). The influent was a mixture of leachate and agriculture wastewater (1:1, v/v), used as the representative high strength wastewater. The bioaugmented and non-bioaugmented systems were operated in parallel, with three levels (low, moderate, and high) of concentrations of organics, nitrogen, and toxic organic compounds in the influent (conditions 1, 2, and 3). The results showed that both systems could efficiently degrade the organic compounds. Nevertheless, the toxic organic compounds biodegradation efficiency of the bioaugmented system was higher than that of the non-bioaugmented one. The bioaugmentation enhanced the overall removal efficiency under conditions 1 and 2. However, the bioaugmented system became less effective under condition 3. Further analysis indicated that the bacterial groups essential to the toxic organic compounds biodegradation were abundant in the aged sludge, including heterotrophic bacteria, heterotrophic nitrifying bacteria, and nitrifying bacteria. The abundance of the effective bacteria improved the biodegradation and wastewater treatment performance of the bioaugmented system. In essence, the aged sludge bioaugmentation is a viable and eco-friendly solution to improving the treatment efficiency of the biological activated sludge system, despite limited biodegradation efficiency in an elevated compounds-concentration environment.

Toxic compounds biodegradation and toxicity of high strength wastewater treated under elevated nitrogen concentration in the activated sludge and membrane bioreactor systems.

This research has assessed the removal efficiencies of toxic compounds in the high strength wastewater (the leachate and agriculture wastewater mixture) using the activated sludge (AS) and membrane bioreactor (MBR) technologies under two carbon to nitrogen (C/N) ratios (C/N 14 and 6) and two toxic compounds concentrations (8-396µg/L and 1000µg/L). In addition, the toxicity evaluations of the AS and MBR effluents to the aquatic environment were undertaken at five effluent dilution ratios (10, 20, 30, 50 and 70% v/v). The findings indicate that the AS treatment performance could be enhanced by the elevation of the nitrogen concentration. Specifically, the C/N 6 environment helps promote the bacterial growth, particularly heterotrophic nitrifying bacteria (HNB) and nitrifying bacteria (NB), which produce the enzymes crucial to the toxic compounds degradation. The improved biodegradation makes the effluents less toxic to the aquatic environment, as evidenced by the lower mortality rates of both experimental fish species raised in the nitrogen-elevated diluted AS effluents. On the other hand, the elevated nitrogen concentration minimally enhances the MBR treatment performance, given the fact that the MBR technology is in itself a biological treatment scheme with very high compounds removal capability. Despite its lower toxic compounds removal efficiency, the AS technology is simple, inexpensive and operationally-friendly, rendering the system more applicable to the treatment operation constrained by the financial, manpower and technological considerations.

Effects of hydraulic retention time and carbon to nitrogen ratio on micro-pollutant biodegradation in membrane bioreactor for leachate treatment.

This research investigated the biodegradation of the micro-pollutants in leachate by the membrane bioreactor (MBR) system under six treatment conditions, comprising two C/N ratios (6, 10) and three hydraulic retention time (HRT) durations (6, 12, 24h). The experimental results indicated that the C/N 6 environment was more advantageous to the bacterial growth. The bacterial communities residing in the sludge were those of heterotrophic bacteria (HB), heterotrophic nitrifying bacteria (HNB) and ammonia oxidizing bacteria (AOB). It was found that HB and HNB produced phenol hydroxylase (PH), esterase (EST), phthalate dioxygenase (PDO) and laccase (LAC) and also enhanced the biodegradation rate constants (k) in the system. At the same time, AOB promoted the production of HB and HNB. The findings also revealed that the 12h HRT was the optimal condition with regard to the highest growth of the bacteria responsible for the biodegradation of phenols and phthalates. Meanwhile, the longer HRT duration (i.e. 24h) was required to effectively bio-degrade carbamazepine (CBZ), N,N-diethyl-m-toluamide (DEET) and diclofenac (DCF).

Biomass production from fermented starch wastewater in photo-bioreactor with internal overflow recirculation.

A photo-bioreactor with internal overflow recirculation was applied to treat real fermented starch wastewater and convert it to photosynthetic biomass for further utilization. The photo-bioreactor was operated at a hydraulic retention time of 10days by circulating mixed liquor through overflow pipes and penetrating light through infrared transmitting filter. During the operation of 154days, the average BOD and COD removals were 95% and 88%, respectively. Majority of photosynthetic bacteria was found attached on pipes as biofilm contributed to 82% of total biomass production. Photosynthetic biomass yield was 0.51g dried solid/g BOD removed and crude protein content of 0.58g/g dried solid. Rhodopseudomonas palustris was found in the photosynthetic system as the predominant bacterial group by denaturing gradient gel electrophoretic analysis (DGGE) and 16S rDNA sequencing method.