Performance Of Vertical Flow Constructed Wetland Research Articles

Laboratory investigation on Bacillus subtilis addition to alleviate bio-clogging for constructed wetlands

Bio-clogging is a major problem in the operation of constructed wetlands (CWs) and is caused by accumulation of biofilm and extracellular polymeric substances (EPS) in the substrate. B. subtilis can successfully produce α-amylase and endoglucanase, which can degrade polysaccharides and, consequently, disperse the EPS. Therefore, the addition of B. subtilis was used to decrease the bio-clogging of lab-scale vertical-flow constructed wetlands (VFCW) in this study, and the feasibility and performance of VFCWs were assessed.The results indicate that the addition of B. subtilis can degrade the polysaccharides in the clogging matter and thereby increase the porosity of the substrate. The hydraulic conductivity of Column 1 (with addition) increased by six times, which was 57 times that of control (Column 2). Meanwhile, the chemical oxygen demand (COD) removal rate also increased after the addition of B. subtilis. The microbial communities show that the richness and diversity within the substrate increased after addition. The relative abundance of functional groups of chemoheterotrophy, aerobic chemoheterotrophy, as well as that connected to N cycles also increased, which implied the improvement of the pollution removal efficiency. Meanwhile, the copy number of α-amylase and endoglucanase increased significantly in Column 1 with the addition of B. subtilis, which offers further support for a hydrolase-induced reduction of polysaccharides and the efficiency of B. subtilis on bio-clogging alleviation. The results showed that B. subtilis addition is an effective and safe solution to control the bio-clogging for CWs. However, further research about long-term effect assessment and dosing strategy optimization should be conducted.

Influence of saturated zone depth and vegetation on the performance of vertical flow-constructed wetland with continuous feeding.

The object of this study was to investigate the effect of saturated zone depth (SZD) and plant on the removal of organics and nitrogen in four continuous-feed vertical flow-constructed wetlands (VFCWs). Three VFCWs were planted with Iris pseudacorus and operated at different SZDs (19, 51, and 84cm), and the other one was non-planted and operated at 51cm SZD. The VFCWs were operated with an organic loading rate (OLR) of 79g chemical oxygen demand (COD)m-2day-1, a total nitrogen loading rate (NLR) of 11g Nm-2day-1, and a hydraulic loading rate (HLR) of 0.35m3m-2day-1. Simultaneous transformation of ammonium and nitrate occurred in all of the four systems. In the planted bed with 51cm SZD, suitable conditions for nitrification and denitrification could be created and the best performance for total nitrogen (TN) removal was realized via simultaneous nitrification and denitrification (SND), achieving TN removal efficiency of 67.4-80.3%. Higher ammonium nitrogen (NH4+-N) and COD removal efficiency was obtained in the system operated with 19cm SZD, whereas higher NO3--N removal could be achieved in the bed with 84cm SZD. With the same SZD of 51cm, the planted VFCW performed preferable removal of COD, NH4+-N, and TN in comparison with the non-planted one. All the VFCWs showed high removal efficiencies for total phosphorus (> 60.15%). Adsorption of phosphorus was primarily observed in the top and upper-middle layers filled with carbon burn slag. It has been proved that the partially saturated VFCW operated with continuous feed could achieve good performance in removal of organic matter and nitrogen by SZD adjustment to develop appropriate aerobic and anoxic regions.

Application of the removal of pollutants from textile industry wastewater in constructed wetlands using fuzzy logic

ABSTRACTThere are more than a hundred textile industries in Turkey that discharge large quantities of dye-rich wastewater, resulting in water pollution. Such effluents must be treated to meet discharge limits imposed by the Water Framework Directive in Turkey. Industrial treatment facilities must be required to monitor operations, keep them cost-effective, prevent operational faults, discharge-limit infringements, and water pollution. This paper proposes the treatment of actual textile wastewater by vertical flow constructed wetland (VFCW) systems operation and monitoring effluent wastewater quality using fuzzy logic with a graphical user interface. The treatment performance of VFCW is investigated in terms of chemical oxygen demand and ammonium nitrogen (NH4-N) content, color, and pH parameters during a 75-day period of operation. A computer program was developed with a fuzzy logic system (a decision- making tool) to graphically present (via a status analysis chart) the quality of treated textile effluent in relation to the Turkish Water Pollution Control Regulation. Fuzzy logic is used in the evaluation of data obtained from the VFCW systems and for notification of critical states exceeding the discharge limits. This creates a warning chart that reports any errors encountered in a reactor during the collection of any sample to the concerned party.