Treatment of municipal wastewater employing constructed wetlands

Abstract

In Bangladesh, water is a growing crisis with the rapidly growing rate of urbanization.Organics,nitrogen,phosphorusandsolidsarecommoncomponentsofwastewatergenerated from urban communities; such wastewater components must be removed priortofinaldisposalforpreventingenvironmentalpollutionandassociatedhumanhealthrisks.Constructed wetlands have been developed into an effective and significant mean oftreatment technology which can be can be employed to provide treatment of municipalwastewater through a complex inter-connected system of plants, media, bulk water andbiomasspopulation.Manystudiesaddressedthree-stagehybridconstructedwetlandconsisted of subsurface wetlands orstructurally modified VF and HF arranged in serieswith an integrated SF-floating to treat municipal wastewater .Thus, there was a scope towork on a potential three-stage hybrid constructed wetland system consisted of verticalflow (VF) and horizontal flow (HF) system arranged in series with an integrated SF orfloatingtreatmentwetlandinconjunctionwithaneffectiveselectionofthelocallyavailablewetland media in treating some major pollutants (organic, nutrients and Coliform) frommunicipalwastewaters priorto disposal inthesurfacewaterbody in Bangladesh.

Total sixteen lab-scale constructed wetland units were built on the roof of the Dr.JamilurRezaChowdhuryCivilEngineeringBhaban,BangladeshUniversityofEngineering and Technology. In total 12 weeks was designed for water logging andstabilizingthesystem;Thestudywasconductedwithintwophases.PhaseIranfor13–24weeksandphasetworanfor25–30weeks.InPhaseI,eightlab-scaleconstructedwetlandunits planted with Canna Indica and 4unplanted vertical constructed wetlands wereoperated individually for treating municipal wastewater treatment. In phase II, pollutantremoval performance was evaluated by four different wetland system trains. Each trainincluded the VF wetland unit (first stage), HF unit (second stage) and SF/ FT unit (finalstage).

In phase I, mean influent concentration of pollutants parameters such as BOD5,COD,ammoniumasNH4-N,TKN,TPandFCwere162mg/l,477.4mg/l,28.8mg/l,54.19mg/l,5.88mg/land65×104(CFU/100ml)respectively.ThemaximumremovalefficiencyofBOD5(98%),COD(95%),ammoniumasNH4-N(98%,),TKN(96%)andTP(96%) were achieved by VF wetland packed with concrete waste. Higher porosity of concretewaste increased retention time and oxygen diffusion inside the media, which improvedorganicremoval,itshighadsorptioncapacitymaintainedNH4–Nattachmentsitesavailability and supported nitrification and the Ca, Al, and Fe contents of concrete wastematerials enhanced P adsorption route.On the other hand, organic media based showedmaximumremovalperformanceofFC(95%).Adsorptionoforganicmatterandbiofilm