Effect of Salinity on Cr(VI) Bioremediation by Algal-Bacterial Aerobic Granular Sludge Treating Synthetic Wastewater

Heavy metal-containing wastewater with high salinity challenges wastewater treatment plants (WWTPs) where the conventional activated sludge process is widely applied. Bioremediation has been proven to be an effective, economical, and eco-friendly technique to remove heavy metals from various wastewaters. The newly developed algal-bacterial aerobic granular sludge (AGS) has emerged as a promising biosorbent for treating wastewater containing heavy metals, especially Cr(VI). In this study, two identical cylindrical sequencing batch reactors (SBRs), i.e., R1 (Control) and R2 (with 1% additional salinity), were used to cultivate algal-bacterial AGS and then to evaluate the effect of salinity on the performance of the two SBRs. The results reflected that less filamentation and a rougher surface could be observed on algal-bacterial AGS when exposed to 1% salinity, which showed little influence on organics removal. However, the removals of total inorganic nitrogen (TIN) and total phosphorus (TP) were noticeably impacted at the 1% salinity condition, and were further decreased with the co-existence of 2 mg/L Cr(VI). The Cr(VI) removal efficiency, on the other hand, was 31–51% by R1 and 28–48% by R2, respectively, indicating that salinity exposure may slightly influence Cr(VI) bioremediation. In addition, salinity exposure stimulated more polysaccharides excretion from algal-bacterial AGS while Cr(VI) exposure promoted proteins excretion.

Response of simultaneous nitrification-denitrification to DO increments in continuously aerated biofilm reactors for aquaculture wastewater treatment

Intensive aquaculture usually produces large volumes of nutrient-rich wastewater, which is essential to treat to avoid eutrophication. This study aimed to evaluate the performance of five, continuously aerated, biofilm reactors treating simulated, high-strength, aquaculture wastewater under different dissolved oxygen (DO) levels, and the effects of DO increments on simultaneous nitrification-denitrification (SND). Continuous aeration was beneficial to complete nitrification. Total inorganic nitrogen (TIN), principally ammonium, was mainly removed by SND. The SND rate response to different DO levels was fitted well by the power function of y = 54.81 + 371.58/(1 − 0.16*x)^(−1/0.24) (R2 = 0.897, P = 0.000). When the TIN was removed completely, the optimal SND rate was defined and corresponded to a value of 121.8%. Accordingly, the optimal DO concentration was calculated as 2.10 mg/L, close to the actual level of 1.83 mg/L, at which the highest proportional removals of total nitrogen (58.0%) and TIN (57.3%) were obtained. Phosphorus was also removed by denitrifying polyphosphate-accumulating organisms.

Direct resource recovery from sewage using a combined system of anaerobic-aerobic biological treatment and food production

A combined system of an anaerobic baffled reactor (ABR), a down-flow hanging sponge (DHS) reactor, an aquarium tank (AT), and a constructed wetland (CWL) was proposed as a new concept for sewage treatment. The ABR and DHS reactor, AT, and CWL were applied for biological sewage treatment, bioassay, and nutrient removal with food production, respectively. Killifishes and tomatoes were cultivated in the AT and CWL, respectively. In the ABR, 81.3% of total chemical oxygen demand and 76.5% of total biochemical oxygen demand were removed at 5.1 h of the hydraulic retention time (HRT). Most remaining organic matter and 47.1% of ammonia were removed in the DHS reactor. In the CWL, 97.0% of total inorganic nitrogen and 78.6% of phosphate were removed with a 3.87 kg/m2 of tomatoes producing yield at 4.4 days of the HRT. In addition, anaerobic ammonium-oxidizing bacteria Candidatus Scalindua and ammonia-oxidizing bacteria Nitrospira and Nitorosococcus were considered as contributors to nitrogen removal in the CWL. The final effluent's water can be utilized as recycled water by installation of sand filtration and disinfection processes. Therefore, the proposed system can be applied as a low-energy, low-cost sewage treatment system with direct resource recovery.

Nutrient cycling and productivity of a Himalayan Glacier Surface

<p>Nutrients deposited and cycled on the glacier surfaces are important not only because of their role in the global biogeochemical cycling in the downstream environments, but also because of their importance as a primary food source for microbes inhabiting glacial surfaces, their ice surface darkening properties, and the consequent potential for enhancing glacier melt. The present study focuses on the Chhota Shigri (CS) Glacier in the North-Western (NW) Indian Himalayan region. The dissolved organic carbon (DOC) concentration in the bare ice is relatively higher than the other aspects studied in the glacial environment of CS indicating that much of the active microbial activity occurring in the bare ice. Total inorganic nitrogen (TIN) is typically concentrated in the snow, which is the major contributor of NO<sub>3</sub><sup>-</sup>. The rapid declining of TIN in the bare ice as compare to other aspects and its enrichment in DOC suggests for a more active microbial activity occurrence in the exposed ice rather than in isolated cryoconites holes in the Chhota Shigri Glacier. The net biological productivity indicates the dominance of net gross photosynthesis over respiration, suggesting a net autotrophic production in CS.</p>

Comparison of hybrid membrane aerated biofilm reactor (MABR)/suspended growth and conventional biological nutrient removal processes

Mathematical modelling was used to investigate the possibility to use membrane aerated biofilm reactors (MABRs) in a largely anoxic suspended growth bioreactor to produce the nitrate-nitrogen required for heterotrophic denitrification and the growth of denitrifying phosphorus accumulating organisms (DPAOs). The results indicate that such a process can be used to achieve a variety of process objectives. The capture of influent biodegradable organic matter while also achieving significant total inorganic nitrogen (TIN) removal can be achieved with or without use of primary treatment by operation at a relatively short suspended growth solids residence time (SRT). Low effluent TIN concentrations can also be achieved, irrespective of the influent wastewater chemical oxygen demand (COD)/total nitrogen (TN) ratio, with somewhat larger suspended growth SRT. Biological phosphorus and nitrogen removal can also be effectively achieved. Further experimental work is needed to confirm these modelling results.

Development of Air Supply Control Technology in Sidestream MLE Process by Measuring Conductivity

Objectives : This study aimed to achieve improved process performance and energy saving by developing a technology to control the air supply of an aerobic basin by measuring the conductivity in the anoxic basin.Methods : To verify whether conductivity can be used as an operation indicator of biological treatment, the correlation analysis between water quality factor and conductivity of each process was conducted by dividing into summer (methanol input), winter and autumn periods. An empirical formula was presented by briefly arranging the required air quantity formula, and a quick reference was prepared by putting air supply in the conductivity range sequentially. The performance evaluation was judged based on the removal efficiency of ammonia nitrogen and total inorganic nitrogen, SNR and SDNR, the change of air supply, the stability of the process against inflow change.Results and Discussion : The seasonal correlation coefficients of conductivity and water quality items were calculated in the order of ammonia nitrogen, total inorganic nitrogen, DOC, and phosphate in the range of 0.5267 ~ 0.9115. It was found that the conductivity could be used as an operation indicator of the biological treatment process with a correlation coefficient of 0.5 or more. The regression equations for the conductivity and ammonia nitrogen are secured by season, so it is possible to estimate the ammonia nitrogen through the conductivity. At the end of the aerobic basin DO was 3.4 mg/L, the nitrogen treatment efficiency in winter was the best. The aerobic basin DO can be controlled by the air supply, and it can be seen that it is possible to control the air supply and improve the nitrogen treatment efficiency by directly measuring the conductivity having a high correlation with nitrogen. An empirical formula for estimating the required air volume through conductivity and inflow is presented. A' and (B' + X') are 0.0589 (m³-air/h)/(m³/h)/(μS/cm) and –77.562 (m³-air/h)/(m³/h). The result of automatic control of air supply according to the measured conductivity of anoxic tank during winter season showed that total inorganic nitrogen removal efficiency and SDNR were 8.3% and 0.007 g-N/g-MLSS/d higher than the actual plant conditions, respectively. During the automatic control period, the air supply/inflow average ratio was 36 (m³-air/h)/(m³/h), which could reduce the air supply by 21.7% compared to the actual plant conditions.Conclusions : The air supply can be estimated from the flow rate and conductivity. The air supply control technology of the conductivity-based MLE process will be able to simultaneously improve nitrogen removal efficiency and reduce energy consumption.

Nitrogen removal and microbial communities of a completely autotrophic nitrogen removal over nitrite (CANON) sequencing batch biofilm reactor (SBBR) at different inorganic carbon (IC) concentrations

In this study, the completely autotrophic nitrogen removal over nitrite (CANON) process was initiated in a sequencing batch biofilm reactor (SBBR). Then the reactor was operated under different IC/N ratios. The total inorganic nitrogen removal efficiency (TINRE) at IC/N ratios of 0.75, 1.0, 1.25, 1.5 and 2.0 were 37.0 ± 11.0%, 58.9 ± 10.2%, 73.9 ± 3.2%, 73.6 ± 1.8% and 72.6 ± 2.0%, respectively. The suitable range of IC/N ratio in this research is 1.25–2.0. The poor nitrogen removal performance at IC/N ratio of 0.75 was due to the lack of growth substrate for AnAOB and low pH simultaneously; at IC/N ratio of 1.0 this was because the substrate concentration was insufficient for fully recovering the AnAOB activities. Microbial analysis indicated that Nitrosomonas, Nitrospira and Candidatus Brocadia were the main ammonium oxidation bacteria (AOB), nitrite oxidation bacteria (NOB) and anammox bacteria (AnAOB), respectively. In addition, at IC ratios of 1.25 or higher, denitrification was promoted with the rise of IC/N ratio, which might be because the change of IC concentrations caused cell lysis of microorganisms and provided organic matter for denitrification.

Advanced treatment of salty eutrophication water using algal-bacterial granular sludge: With focus on nitrogen removal, phosphorus removal, and lipid accumulation

A new algal-bacterial granular sludge treatment method was used to treat salty eutrophication water. The results indicated that the treatment removed more than 98% of the total inorganic nitrogen and the total phosphorus after a 15 d cultivation period using 2% salinity simulated eutrophication water. For the 4% salinity simulated water, the total phosphorus was not able to be removed and was even higher in the effluent; and the total inorganic nitrogen was only removed 17%. Thus, the algal-bacterial granules were efficient for removing nitrogen and phosphorus in 2% salinity eutrophication water but were not effective for 4% salinity water. High levels of filamentous algae proliferation growing on the surface of the granules was primarily responsible for the good performance in 2% salinity water. However, the lipid accumulation was greatly enhanced (reactor R2 at a 27.6% increase and reactor R4 at a 107% increase) for both granule types due to the algal growth. Thus, treatment of the salty eutrophication water can also greatly increase the added-value of the algal-bacterial granules.

Comparative Analysis of Hydrogenotrophic Denitrification in up and down Flow Reactors

Use of ground water containing ammonical nitrogen has been increasing in Kathmandu valley. The use of locally and cheaply fitted Hydrogenotrophic Denitrification (HD) has been taken as an effective way to remove the nitrates in this study. Comparative analysis of HD reactors had been studied for the determination of the effective flow direction of water as Up Flow or Down Flow. The result reviled that flow direction as Down Flow HD reactor performed slightly better than Up Flow HD reactor. The maximum NO3-N conversion reached 100% for Down Flow and 98.65% for Up Flow reactor with maximum of total inorganic nitrogen (TIN) removed were 41.11% and 33.89% for Down Flow and Up Flow reactor respectively. The difference in NO3-N conversion and TIN removal were observed. As the NO2-N was accumulated, suggesting NO3 conversion is higher than NO2 conversion thus, and majorly incomplete denitrification existed. The NO2-N in water reached to maximum of 78.89 mg/l and 72.55 mg/l for Down Flow and Up Flow rector.