Abstract
Constructed wetlands (CWs) have been used globally in wastewater treatment for years. CWs represent an efficient ecological system which is both energy-saving and low in investment for construction and operational cost. In addition, CWs also have the advantage of being easy to operate and maintain. However, the operation of CWs at northern latitudes (both mid and high) is sometimes quite demanding, due to the inhibitory effect of low temperatures that often occur in winter. To evaluate the wastewater treatment performance of a culture of mixed Psychrotrophic bacteria strains in an integrated vertical-flow CW, the removal rates of ammonia nitrogen (NH3–N), chemical oxygen demand (COD), nitrite nitrogen , nitrate nitrogen and total phosphorus (TP) were quantified at different bacterial dosages to determine the best bacterial dosage and establish kinetic degradation models of the mixed strains. The bacterial culture was made up of Psychrobacter TM-1, Sphingobacterium TM-2 and Pseudomonas TM-3, mixed together at a volume/volume ratio of 1 : 1 : 1 (at bacterial suspension concentrations of 4.4 × 109 ml−1). Results showed that the organic pollutants (nitrogen and phosphorus) in the sewage could be efficiently removed by the culture of mixed Psychrotrophic bacteria. The optimal dosage of this mixed bacteria strain was 2.5%, and the treatment efficiency of COD, NH3–N, , , total nitrogen and TP were stable at 91.8%, 91.1%, 88.0%, 93.8%, 94.8% and 95.2%, respectively, which were 1.5, 2.0, 2.1, 1.5, 2.2 and 1.3 times those of the control group. In addition, a pseudo-first-order degradation model was a good fit for the degradation pattern observed for each of these pollutants.
Highlights
A constructed wetland (CW) is an artificial wetland built to imitate a natural wetland ecosystem
It was found that the contaminant removal rate by CWs could reach 85% to 95% for biochemical oxygen demand (BOD), 80% for chemical oxygen demand (COD) and 92.41% for nitrogen compounds [9]
This is because microbial activity is reduced as the water temperature decreases, and the biological activity of CWs might decrease under winter conditions
Summary
A constructed wetland (CW) is an artificial wetland built to imitate a natural wetland ecosystem. It was found that the contaminant removal rate by CWs could reach 85% to 95% for biochemical oxygen demand (BOD), 80% for chemical oxygen demand (COD) and 92.41% for nitrogen compounds [9]. The main mechanisms of pollutant removal in constructed wetlands involve several biological processes (e.g. microbial metabolic activity and plant uptake) and physico-chemical processes (e.g. sedimentation, adsorption and precipitation at water-sediment, root-sediment and plant–water interfaces) [10]. The sewage treatment efficiency of the constructed wetlands in northern China is rather low in winter. This is because microbial activity is reduced as the water temperature decreases, and (due to winter plant death) the biological activity of CWs might decrease under winter conditions. Thereby the pollutant removal efficiency and, more importantly, the efficacy of this contaminant removal technique might be affected by seasonal changes
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