Removal Of Carbon-containing Organic Matters In The Subsurface Flow Constructed Wetlands And Affecting Factors

The organic matter in water has always attracted the attention of researchers. Generally, the total organic carbon (TOC) comes from natural and anthropic sources. Even if it is not directly responsible for dangers on human health, its determination is important for various water body. It contributes significantly to acidity of waters through organic acids, biological activities through the absorption of light, and water chemistry through the complexation of metals and production of carcinogenic compounds with chlorine. In addition, by forming organic complexes, organic carbon can influence nutrient availability and control the solubility and toxicity of contaminants.This subject evaluates the effect of hydraulic loading rate (HLR), aspect ratio, granular medium size, season and water depth on the fate of carbon-containing organic matters in a pilot-scale subsurface flow constructed wetlands (SSF) over a period of 2 years. Emphasis was placed on the effect of characteristics of incoming wastewater on carbon-containing organic matters removal and its mechanism. The main results are as following:1. Water samples collected from Sept. 2005 to Sept. 2007 were analyzed, average results showed that the pilot-scale subsurface constructed wetlands system removed 7%, 16%, 63%, 73%,65% and 87%, of TN, TP, COD, BOD and TSS, respectively. The bed with low water. level and finer gravels showed good performance under optimum conditions with a 3-d HRT, in which 10% TN, 19% TP, 67% TOC, 89.3% TSS removal can be reached.2. Hydraulic loading rate (HLR) and season are major factors in controlling the performance of constructed wetlands system, while aspect ratio, water depth and granular medium size have no clear effect on the removal of contaminants in the range of operational conditions tested. The season caused significant statistical differences in the average effluent TOC concentrations (p<0.01). The HLR caused significant statistical differences in the average effluent TOC concentration (p<0.01). Hence, HLR and season are two important factors controlling the performance of constructed wetlands system for TOC removal. 3. The influent linear alkylbenzene sulfonates (LAS) loading in the wastewater caused important effect on the fate of carbon in the constructed wetlands system. Results show that gaseous carbon, TOC, acetic acid and volatile fatty acids removal rate increase with increase of influent LAS loading in the constructed wetlands system.4. Results of redox potential survey show very reducing conditions in constructed wetlands system. Coupled with a theoretical estimation of electron acceptors (such as SO₄^2-, NO₃^- and NO₂^-) to the oxidation of organic matter in the constructed wetlands system, it is highly possible that organic matter is mainly removed through methanogenesis in the present constructed wetlands system.This research was supported by the National Natural Science foundation of China "Study on the degradation of organic contaminants in the constructed wetlands treating wastewater" (No.20477033) and the National Natural Science foundation of Chongqing (No. 2004BA7019).