Studies on Wastewater Treatment by Means of Integrated Biological Pond System: Design and Function of Macrophytes

A biological treatment pond system to purify municipal wastewater from a medium-sized city has been operated for 3 years and gained good results. Macrophytes took a very important part in this system. The macrophyte ponds and zones were designed spacially and periodically different to test their purification efficiencies.The purifing system was divided into three functional zones: purifing zone, effluent upgrading zone and multi-utilization zone. Macrophytes were planted in several subzones in series in some ponds. The experiments showed that the multi-macrophyte zone system revealed greater purification efficiencies than those of traditional oxidation ponds as well as general macrophyte ponds. The system reached high reductions of COD, BOD, TSS, TN and TP. The activity of mutagenic agents and numbers of virus and bacteria were significantly decreased during the process of purification. The effluent from the system was greatly upgraded and could be used in fishery and agriculture. The harvested macrophytes from the purifing zone and effluent upgrading zone could be put into the multi-utilization zone as feed, fertilizer, biogas, etc. The idea of resourcization of wastewater was being put into practice. The studies also showed that some macrophytes revealed strong ability to inhibit algae growth not because of light, nutrient and space competition. These results had been used in the treatment system design and gained expected effects. Plant harvesting did not yield dramatic effects on reductions of the main pollutants, though it did affect remarkably the biomass productivity of the macrophytes.