Enhanced Nitrogen And Phosphorus Removal From Domestic Wastewater By Anactivated Sludge Process Combined With Vegetation

A hybrid wastewater treatment process comprised of an activated sludge processand vegetations, termed as vegetation-activated sludge process (V-ASP), was proposed,not only to satisfy the requirement of decentralized domestic wastewater treatment, butalso to make up the problems encountered in conventional ecological sewage treatmenttechnologies, such as unstable treatment efficiency, low landscape effects, and largefootprint. The V-ASP system was developed based on the Living Machine (LM) andFBR technology. The vegetations were selected based on their enhanced nitrogen andphosphorus removal capabilities, and were configured to conventional A2O afterestimation of the effects by the operational conditions. The results herein give the directguideline for ecological decentralization wastewater treatment with high landscapefunction, and/or bring about the fundamental understanding of nutrients removal oruptake function by different vegetations that would be employed to sewage treatmenttechonologies.The suitable vegetations for V-ASP process were selected on the basis of thenutrients removal capabilities. Two major vegetation categories, traditional ornamentalvegetations (named as Type I) and conventional sophisticated vegetations in ecologicalwastewater treatment station (Type II), were employed in series of batch tests. Theresults showed that the NH4+-N, NO3--N and TP removal efficiency by Type Ivegetation ranged about7.4%~21.5%,20.4%~35.5%and16.1%~32.0%, respectively.The maximum pollutants removal efficiencies were achived bySpathiphyllum kochii,followed by Anthurium andraeanum, Dracaena sanderiana, Calathea freddy, Alocasiamacrorrhiza, Philoclendron’con-go’and Syngonium poclphyllum. In comparison, theNH4+-N, NO3--N and TP removal efficiency by Type IIvegetation wasabout7.1%~13.8%、29.9%~39.0%and26.7%~34.0%, respectively, whose average efficiencywas slightly higher than the Type I did. Considering the enhanced nitrogen andphosphorusremoval efficiency by vegetation, a vegetations selection evaluation system,including their adaptability, tolerance, landscape and other factors, was established toinstruct the V-ASP configuration. Through a comprehensive comparison on parametersindicators and their contribution factor, the Type I vegetation that preferred to combinewith A2O includes Spathiphyllum kochii, Anthurium andraeanum,Dracaena sanderianaandCalathea freddy, whilst the Type II vegetation was Canna genaralis,Pontederiacordata L., Cyperus alternifoliusand Dracaena sanderiana.The configurative modes of V-ASP system focused on vegetation installation andcollocation to the conventional A2O were determine, according to the vegetation nutrients removal and influential factors. Two dissolved oxygen (DO) concentrations(0.5and2mg/L) in the reactor, which was believed as the crutial factor for vegetationconfiguration, were selected to evaluate their impact onto nutrients removalperformance. It was found that high DO likely to improve the nutrients removalefficiency by Canna genaralis, Cyperus alternifolius, Anthurium andraeanumandSpathiphyllum kochii, in which Canna genaralisand Cyperus alternifolius, could elevateTN removal efficiency by14.8%and19.2%, respectively. However, DO changedisplayed limited effect onto Dracaena sanderiana, while had remarkably inhibitioneffect on Pontederia cordata L. In addition, a high DO would promot the DIP removalefficiency of Canna genaralis, but showed a little effect on TP removal. However, highDO had inhibition effect on the other plants, leading to the removal efficienciesdecreased more than5.3%~11.8%. The nutrients removal performance did also correlatewith other operational conditions, e.g. hydraulic retention time (HRT). Therefore, thevegetation prefer to configurate to the anaerobic and anoxic tank were Canna genaralis,Pontederia cordata L., Dracaena sanderiana, Cyperus alternifolius, Spathiphyllumkochii and Anthurium andraeanum, while those would prefer to install to the aerobictank were Canna genaralis, Cyperus alternifolius, Dracaena sanderiana, Spathiphyllumkochii and Anthurium andraeanum.The V-ASP system based on the experimental results was developed, and itspollutants removal performance from domestic wastewater and stability wereinvestigated in a pilot-scale experiment. It was observed that the NH4+-N and TNremoval efficiency in V-ASP system was97.6%and83.6%, respectively, both of whichwere rather comparable with the conventional A2O system. In contrast, their TP andCOD removal efficiency averaged around92.8%and88.9%, respectively, which wasstably higher than the conventional A2O system. The V-ASP system could consistentlyproduce the effluent stasfied the discharge standard Class1-A of municipal waste watertreatment plant (GB18918-2002), which gave practical experience and technical supportfor the development of ecological decentralized wastewater treatment techonologies.