Yuansheng Hu

High rate nitrogen removal in an alum sludge-based intermittent aeration constructed wetland

A new development on treatment wetland technology for the purpose of achieving high rate nitrogen removal from high strength wastewater has been made in this study. The laboratory scale alum sludge-based intermittent aeration constructed wetland (AlS-IACW) was integrated with predenitrification, intermittent aeration, and step-feeding strategies. Results obtained from 280 days of operation have demonstrated extraordinary nitrogen removal performance with mean total nitrogen (TN) removal efficiency of 90% under high N loading rate (NLR) of 46.7 g N m(-2) d(-1). This performance was a substantial improvement compared to the reported TN removal performance in literature. Most significantly, partial nitrification and simultaneous nitrification denitrification (SND) via nitrite was found to be the main nitrogen conversion pathways in the AlS-IACW system under high dissolved oxygen concentrations (3-6 mg L(-1)) without specific control. SND under high dissolved oxygen (DO) brings high nitrogen conversion rates. Partial nitrification and SND via nitrite can significantly reduce the demand for organic carbon compared with full nitrification and denitrification via nitrate (up to 40%). Overall, these mechanisms allow the system to maintaining efficient and high rate TN removal even under carbon limiting conditions.

Looking Beyond Struvite for P-Recovery

) and could potentially be used asa slow-release fertilizer. If the economic and life cycle costs aretaken into account, however, it becomes clear that phosphaterecovery as struvite is likely not the best approach, for thefollowing reasons: (1) production of P-mineral with a highcontent of struvite from real wastewater is a difficult and costlyprocess; and (2) struvite is not superior to other phosphate-based compounds in fertilization efficiency, nor is it an exclusiveform of raw materials favored by the fertilizer industry.In literature and practice, struvite precipitation is usuallyperformed under alkaline conditions, which are created bydosing alkalinity or CO

A review of a recently emerged technology: constructed wetland - microbial fuel cells.

Constructed wetlands (CWs) and microbial fuel cells (MFCs) are compatible technologies since both are reliant on the actions of bacteria to remove contaminants from wastewater. MFCs require the anode to remain anaerobic with the cathode exposed to oxygen while these redox conditions can develop naturally in CWs. For this reason, research into combining the two technologies (termed as CW-MFC) has emerged in recent years with the aim of improving the wastewater treatment capacity of wetlands while simultaneously producing electrical power. Based on the published work (although limited), this review aims to provide a timely, current state-of-the-art in CW-MFC while exploring future challenges and research directions.

The integrated processes for wastewater treatment based on the principle of microbial fuel cells: A review

abstract Microbial fuel cell (MFC) technology offers the dual advantages of wastewater treatment and electricity generation. Research efforts have been made to improve its power output. However, MFC seems limited at pilot scale and power outputs appear to have plateaued. As such, some integrated technologies have emerged based on MFC. These hybrid technologies have the larger potential for scaling up and practical application compared with the pure MFC. Therefore, in their review the authors present these emerged technologies and discuss the development tendency and the challenges. The review can hopefully provide a framework to identify priorities for further research on this area.

Comprehensive analysis of step-feeding strategy to enhance biological nitrogen removal in alum sludge-based tidal flow constructed wetlands.

Step-feeding strategies have been extensively studied and comprehensively analyzed in this study for a four-stage alum sludge-based tidal flow constructed wetlands (AlS-TFCWs) system. Enhanced total nitrogen removal of 83% is achieved under high nitrogen loading rate of 19.1 g N/m(2)d. The key issues towards the success of a significant nitrogen removal in step-feeding TFCWs are the bed resting time (which provides better aeration for nitrification) and up flow stage/delayed input of side stream(s) (which ensure favorable environment for better denitrification). Simultaneous nitrification and denitrification (SND) was found effective in the 1st stage of the system and SND via nitrite is the main nitrogen conversion mechanism. The optimal influent distribution fraction for step-feeding purpose can be estimated from a theoretical basis, which is a function of the influent BCOD/TKN ratio. Therefore the influent distribution fraction should be adjusted according to the variety of influent characteristics, rather than a fixed value.

Performance evaluation and prediction for a pilot two-stage on-site constructed wetland system employing dewatered alum sludge as main substrate

Dewatered alum sludge, a widely generated by-product of drinking water treatment plants using aluminium salts as coagulants was used as main substrate in a pilot on-site constructed wetland system treating agricultural wastewater for 11 months. Treatment performance was evaluated and spreadsheet analysis was used to establish correlations between water quality variables. Results showed that removal rates (in g/m(2)d) of 4.6-249.2 for 5 day biochemical oxygen demand (BOD(5)), 35.6-502.0 for chemical oxygen demand (COD), 2.5-14.3 for total phosphorus (TP) and 2.7-14.6 for phosphate (PO(4)P) were achieved. Multiple regression analysis showed that effluent BOD(5) and COD can be predicted to a reasonable accuracy (R(2)=0.665 and 0.588, respectively) by using input variables which can be easily monitored in real time as sole predictor variables. This could provide a rapid and cheap alternative to such laborious and time consuming analyses and also serve as management tools for day-to-day process control.

Promoting the bio-cathode formation of a constructed wetland-microbial fuel cell by using powder activated carbon modified alum sludge in anode chamber.

MFC centered hybrid technologies have attracted attention during the last few years due to their compatibility and dual advantages of energy recovery and wastewater treatment. In this study, a MFC was integrated into a dewatered alum sludge (DAS)- based vertical upflow constructed wetland (CW). Powder activate carbon (PAC) was used in the anode area in varied percentage with DAS to explore its influences on the performance of the CW-MFC system. The trial has demonstrated that the inclusion of PAC improved the removal efficiencies of COD, TN and RP. More significantly, increasing the proportion of PAC from 2% to 10% can significantly enhance the maximum power densities from 36.58 mW/m2 to 87.79 mW/m2. The induced favorable environment for bio-cathode formation might be the main reason for this improvement since the content of total extracellular polymeric substances (TEPS) of the substrate in the cathode area almost doubled (from 44.59 μg/g wet sludge to 87.70 μg/g wet sludge) as the percentage of PAC increased to 10%. This work provides another potential usage of PAC in CW-MFCs with a higher wastewater treatment efficiency and energy recovery.

On the fit of statistical and the k-C* models to projecting treatment performance in a constructed wetland system.

The objective of this study was to assess the suitability of statistical and the k-C* models to projecting treatment performance of constructed wetlands by applying the models to predict the final effluent concentrations of a pilot field-scale constructed wetlands system (CWs) treating animal farm wastewater. The CWs achieved removal rates (in g/m2.d) ranging from 7.1–149.8 for BOD5, 49.8–253.8 for COD and 7.1–47.0 for NH4-N. Generally, it was found that the statistical models developed from multiple regression analyses (MRA) were stronger in predicting final effluent concentrations than the k-C* model. However, both models were inadequate in predicting the final effluent concentrations of NO3-N. The first-order area-based removal rate constants (k, m/yr) determined from the experimental data were 200.5 for BOD5, 80.1 for TP and 173.8 for NH4-N and these indicate a high rate of pollutant removal within the CWs.

Nitrogen dynamics model for a pilot field-scale novel dewatered alum sludge cake-based constructed wetland system

A model simulating the effluent nitrogen (N) concentration of treated animal farm wastewater in a pilot on-site constructed wetland (CW) system, using dewatered alum sludge cake (DASC) as wetland substrate, is presented. The N-model was developed based on the Structural Thinking Experiential Learning Laboratory with Animation software and is considering organic nitrogen, ammonia nitrogen (NH3) and nitrate nitrogen (NO3-N) as the major forms of nitrogen involved in the transformation chains. Ammonification (AMM), ammonia volatilization, nitrification (NIT), denitrification, plant uptake, plant decaying and uptake of inorganic nitrogen by algae and bacteria were considered in this model. pH, dissolved oxygen, temperature, precipitation, solar radiation and nitrogen concentrations were considered as forcing functions in the model. The model was calibrated by observed data with a reasonable agreement prior to its applications. The simulated effluent detritus nitrogen, NH4-N, NO3-N and TN had a considerably good agreement with the observed results. The mass balance analysis shows that NIT accounts for 65.60%, adsorption (ad) (11.90%), AMM (8.90%) followed by NH4-N (Plants) (5.90%) and NO3-N (Plants) (4.40%). The TN removal was found 52% of the total influent TN in the CW. This study suggested an improved overall performance of a DASC-based CW and efficient N removal from wastewater.