Ultrashort Hydraulic Retention Time of Aeration and Nonaeration Constructed Wetlands for a Large Volume of Primary-Treated Wastewater from a Medical Rubber Glove Factory

Abstract

A substantial volume of primary-treated wastewater from a medical rubber glove factory caused public freshwater to become sewage. The ultrashort hydraulic retention time in constructed wetlands was urgently employed for wastewater remediation. Pilot-scale, aeration, and nonaeration horizontal surface flow constructed wetlands (HSFCWs) with emergent plants were designed, compared, and optimized. Activated carbon, coconut shells, and oyster shells were subsequently transferred into a plastic basket as a substrate layer, while Typha angustifolia L. was used as an emergent plant. The experiments were conducted at a hydraulic retention time of 2, 4, 6, and 8 hr. per effluent recirculation. Sampling data were collected for each of the four effluent recirculations. The removal efficiencies of BOD, COD, FOG, TKN, TSS, TDS, EC, and salinity in the aeration HSFCWs were high—53.25, 67.28, 97.93, 78.93, 95.87, 87.52, 86.36, and 90.38%—at the first effluent recirculation of sampling, respectively, while the removal efficiencies in the nonaeration HSFCWs were also high—55.12, 57.38, 94.62, 83.10, 95.95, 88.09, 89.54, and 93.46%, respectively. Increasing the hydraulic retention time increased removal efficiencies. The removal efficiency of BOD in aerated HSFCWs was higher than in nonaerated HSFCWs in the second effluent recirculation of sampling. This is because the oxygen supplied by aeration in the system increased the organic and inorganic pollutant removal efficiencies. Other pollutants were removed more effectively during the second effluent recirculation. Excluding BOD and COD, Duncan’s multiple test revealed that the number of effluent recirculations for removal efficiencies of FOG, TKN, TSS, TDS, EC, and salinity was nonsignificant at the p ≤ 0.001 level. These findings led to optimization of the medical rubber glove wastewater treatment at an ultrashort hydraulic retention time of 2–4 hr. This process and the control of CWs may be the best industrial wastewater treatment practice and a long-term solution for the industrial sector.