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Stanford CEE 215 - Technical Note Influence of COD

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Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 83:756–762 (2008)Technical NoteInfluence of COD:N:P ratio on darkgreywater treatment using a sequencing batchreactorVijayaraghavan Krishnan, Desa Ahmad∗and Juriah Binti JeruDepartment of Biological & Agricultural Engineering, Faculty of Engineering, University Putra Malaysia, 43400 UPM Serdang, Selangor,MalaysiaAbstract: The recycling of greywater is an integral part of a water management system owing to the scarcity offresh water resources. This article explores the effectiveness of an aerobic sequencing batch reactor in treatingnutrient-deficit and nutrient-spiked dark greywater for agricultural reuse. The dark greywater in the presentinvestigation had a COD:N:P ratio of 100:1.82:0.76, while the preferred ratio for biological oxidation is 100:5:1(COD, chemical oxygen demand). The aerobic oxidation of nutrient-deficit and nutrient-spiked dark greywaterwith a COD:N:P ratio of 100:2.5:0.5; 100:3.5:0.75 and 100:5:1 resulted i n outlet COD values of 64; 35; 15 and12 mg L−1, with a corresponding BOD5value of 37; 22; 10 and 8 mg L−1at 36 h hydraulic retention time (HRT).Hence treatment of nutrient-added dark greywater at a COD:N:P ratio 100:3.5:0.75 and 100:5:1 for 36 h HRTcomplied with the Malaysian discharge standards for agricultural activities. Treated greywater has the potentialfor consideration as a resource, since it can be used as a supplement or replacement for potable water in landscapeirrigation and other agricultural activities in rural and urban areas. Moreover, the level of greywater treatment isdictated by the final water quality requirement. 2008 Society of Chemical IndustryKeywords: dark greywater; sequencing batch reactor; kitchen wastewater; COD:N:P ratio; aerobic processINTRODUCTIONWastewaters generated in residential areas can beclassified into two types; namely blackwater andgreywater. Black water is wastewater generated fromtoilet systems; greywater is wastewater generatedfrom the kitchen, washing machines and washroomsexcluding toilet flushing. Greywater was furtherclassified into two types, depending on the generatingsource. Wastewater generated from bathroom sinks,baths and showers was classified as ‘light greywater’.Whereas wastewater generated from laundry facilities,dishwashers and kitchen sinks was classified as ‘darkgreywater’.1Compared to blackwater, dark greywater usuallycontains less nutrients and breaks down much morerapidly in the environment. Dark greywater is thusunlikely to cause severe pollution. Adapting naturalprocesses to human technology needs has resultedin such treatment processes as phytoremediation,rock-reed filter systems, greywater systems, blackwatersystems, biological treatment areas, and constructedwetlands. The reuse of wastewater on planted areasis nothing new to agrarian cultures: it is documentedthat English and German farmers used wastewater asfertilizer as early as the 16th century. Early Greeksdid the same, as did people in many Asian countrieseven before the days of Plato. Greywater contributes50–80% of the average total volume of water usedin the home. In many areas of the world that arefacing severe water shortages, greywater is an attractivealternative for reuse outdoors, to water ornamentalplanting beds or lawns. Greywater is a valuable on-siteresource, which conserves precious drinking water,reduces the load on wastewater disposal systems,recharges dwindling groundwater supplies, enhancesplant growth, and reuses vital nutrients. Reusinggreywater for garden irrigation should be encouragedin both urban and rural households.2,3One of the main drawbacks of dark greywater forbiological treatment units is the limitation on majornutrients like nitrogen and phosphate. In the presentinvestigation, the raw dark greywater had a COD:N:Pratio of 100:1.82:0.76, while the preferred ratio forbiological oxidation is 100:5:1. The observed nutrient-deficiency confirmed earlier research, which foundCOD:N:P ratios of 100:1.64:1.284and 168:0.8:2.4.5In general, every organism must find in its environmentall of the substances required for energy generation andcellular biosynthesis. The chemicals and elements ofthis environment that are utilized for bacterial growth∗Correspondence to: Desa Ahmad, Department of Biological & Agricultural Engineering, Faculty of Engineering, University Putra Malaysia, 43400 UPMSerdang, Selangor, MalaysiaE-mail: [email protected](Received 16 July 2007; revised version received 19 October 2007; accepted 24 October 2007)Published online 5 February 2008; DOI: 10.1002/jctb.1842 2008 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2008/$30.00Influence of COD:N:P ratio on greywater treatmentare referred to as nutrients. Carbon, nitrogen andphosphate are considered to be the major nutrients.On average, carbon accounts for 50% of the dry weightof cellular material, and it is the main constituent.Nitrogen accounts for 14% of the dry weight and it isa constituent of aminoacids, nucleic acids, nucleotidesand coenzymes. Phosphorus accounts for 3% of dryweight and is found in nucleic acids, nucleotides,phospholipids and teichoic acids.6The concept of recycling greywater in toilet flushingwas also investigated after subjecting it to biologicaltreatment and chlorination,7filtration, sedimentationand disinfection using hypochlorite.8Lazarova et al.9summarized the water quality of reclaimed urbanwater with reference to its application in toiletflushing. Jeppesen10stated that even though greywateris presumed to be free from fecal contamination,when mixed with wash room wastewater thereis a greater possibility of the presence of fecalcoliform. The diurnal variation in domestic wastewatervolume and its quality was investigated by Almeidaet al., (1999)11and Butler et al., (1995).12Thecharacteristics of greywater were investigated byPalmquist and Hanaeus (2005),6while Erikssonet al., (2002)13reviewed the greywater characteristicsoriginating from different sources. The effect of storageon untreated greywater was investigated by Dixon et al.(1999).14Elke et al. (2003)15highlighted the potentialof greywater treatment and its reuse in rural areas withrespect to treatment method and operational cost.The biological treatment of greywater has beeninvestigated using a sequencing batch reactor andmicrofiltration process,16rotating biological contactor(RBC) and fluidized bed reactor,17RBC andmembrane bioreactor (MBR),18and


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Stanford CEE 215 - Technical Note Influence of COD

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