Chemosphere 66 2007 916 923 www elsevier com locate chemosphere Recycled vertical ow constructed wetland RVFCW a novel method of recycling greywater for irrigation in small communities and households A Gross a a O Shmueli a Z Ronen a E Raveh b Department of Environmental Hydrology and Microbiology Zuckerberg Institute for Water Research Jacob Blaustein Institutes for Desert Research Ben Gurion University of the Negev Sede Boqer Campus 84990 Midreshet Ben Gurion Israel b Department of Plant Science Gilat Research Center Mobile Post Negev 85280 Israel Received 19 February 2006 received in revised form 4 June 2006 accepted 6 June 2006 Available online 17 July 2006 Abstract The use of greywater for irrigation is becoming increasingly common However raw greywater is often contaminated and can cause environmental harm and pose health risks Nevertheless it is often used without any signi cant pretreatment a practice mistakenly considered safe The aim of this study was to develop an economically sound low tech and easily maintainable treatment system that would allow safe and sustainable use of greywater for landscape irrigation in small communities and households The system is based on a combination of vertical ow constructed wetland with water recycling and trickling lter and is termed recycled vertical ow constructed wetland RVFCW The RVFCW s properties removal e ciency hydraulic parameters and feasibility were studied as well as the environmental e ects of the treated greywater as re ected by soil and plant parameters over time The RVFCW was e cient at removing virtually all of the suspended solids and biological oxygen demand and about 80 of the chemical oxygen demand after 8 h Fecal coliforms dropped by three to four orders of magnitude from their initial concentration after 8 h but this was not always enough to meet current regulations for unlimited irrigation The treated greywater had no signi cant negative impact on plants or soil during the study period The feasibility analysis indicated a return over investment after approximately three years We concluded that the RVFCW is a sustainable and promising treatment system for greywater use that can be run and maintained by unskilled operators 2006 Elsevier Ltd All rights reserved Keywords Vertical ow constructed wetland Wastewater reuse Greywater treatment Environmental pollution 1 Introduction The quantity of freshwater available worldwide is declining raising the pressing need for its more e cient use One method of conserving water is by recycling greywater GW for irrigation GW is domestic wastewater that includes only wash water i e bath dish and laundry water whereas blackwater consists of toilet water Due to the substantial di erence in their qualities separating GW and blackwater would provide for more e ective wastewater treatment allowing a large volume of water Corresponding author Tel 972 8 6596896 fax 972 8 6596909 E mail address amgross bgumail bgu ac il A Gross 0045 6535 see front matter 2006 Elsevier Ltd All rights reserved doi 10 1016 j chemosphere 2006 06 006 to be e ciently recycled Lindstrom 2000 This is particularly important in arid zones were water is scarce and recycling GW for private and public landscape irrigation could reduce potable water use by up to 50 DHWA 2002 The use of GW for private garden irrigation is becoming increasingly common In most countries regulations or speci c guidelines for GW reuse are not available and it is therefore often used without any signi cant pretreatment a practice mistakenly considered safe In countries such as the USA and Australia where regulations for the use of GW have been established they concentrate on issues associated with public health but do not consider potential harmful environmental impacts Dixon et al 1999 DHWA 2002 ADEQ 2003 The separation of the A Gross et al Chemosphere 66 2007 916 923 917 toilet stream from domestic wastewater generates e uents which have reduced levels of nitrogen solids and organic matter especially the barely degradable fraction but often contain elevated levels of surfactants oils boron and salt The components in GW may alter soil properties damage plants and contaminate groundwater Garland et al 2000 Gross et al 2005 Wiel Shafran et al 2006 A study aimed at applying commercial systems to GW reuse in households demonstrated in ve di erent commercial systems failure to treat the GW su ciently for unlimited use Gross et al 2003 That study also suggested that this was so either because the treatment was too super cial as the water is considered safe by many or because it was a downscaled wastewater treatment system rather than a GW treatment system aimed at treating small volumes in private houses The aim of the current study was to develop an economically sound low tech and easy maintenance treatment system that would allow safe and sustainable use of GW for landscape irrigation in small communities and households 2 Materials and methods 2 1 Recycled vertical ow constructed wetland The proposed treatment method is a modi cation of the vertical ow constructed wetland VFCW described by IWA 2000 with a novel set up Initially the system was composed of two containers 0 95 m W 0 95 ml 0 55 mH about 500 l each placed one above the other 1 the upper one was a VFCW composed of a three layer bed consisting of 15 cm planted organic soil over a 30 cm layer of tu or plastic media and a 5 cm lower layer of limestone pebbles The bottom of the bed s compartment was perforated 2 the lower container was used as a water reservoir located directly beneath the VFCW Fig 1 The raw GW owed through a sedimentation tank which accounted for about 10 of the total system volume and where only coarse material settled From this tank it was pumped or over owed into the root zone of the VFCW plants and then it trickled down through the three layer lter bed to the reservoir A centrifuge pump continuously recycled the GW at a known rate from the reservoir back to the VFCW The treated water was then used for irrigation directly or following a secondary sedimentation An over ow pipe was set from the upper wetland container to the reservoir to prevent over ow in case of the wetland clogging 2 2 Recycled vertical ow constructed wetland performance The Recycled vertical ow constructed wetland RVFCW properties removal e ciency and hydraulic parameters were studied in a short term study a 3 month batch greenhouse study and a long term case study All the studies were
View Full Document
Unlocking...