Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 83 756 762 2008 Technical Note Influence of COD N P ratio on dark greywater treatment using a sequencing batch reactor Vijayaraghavan Krishnan Desa Ahmad and Juriah Binti Jeru Department of Biological Agricultural Engineering Faculty of Engineering University Putra Malaysia 43400 UPM Serdang Selangor Malaysia Abstract The recycling of greywater is an integral part of a water management system owing to the scarcity of fresh water resources This article explores the effectiveness of an aerobic sequencing batch reactor in treating nutrient deficit and nutrient spiked dark greywater for agricultural reuse The dark greywater in the present investigation 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 greywater with a COD N P ratio of 100 2 5 0 5 100 3 5 0 75 and 100 5 1 resulted in outlet COD values of 64 35 15 and 12 mg L 1 with a corresponding BOD5 value of 37 22 10 and 8 mg L 1 at 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 HRT complied with the Malaysian discharge standards for agricultural activities Treated greywater has the potential for consideration as a resource since it can be used as a supplement or replacement for potable water in landscape irrigation and other agricultural activities in rural and urban areas Moreover the level of greywater treatment is dictated by the final water quality requirement 2008 Society of Chemical Industry Keywords dark greywater sequencing batch reactor kitchen wastewater COD N P ratio aerobic process INTRODUCTION Wastewaters generated in residential areas can be classified into two types namely blackwater and greywater Black water is wastewater generated from toilet systems greywater is wastewater generated from the kitchen washing machines and washrooms excluding toilet flushing Greywater was further classified into two types depending on the generating source 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 dark greywater 1 Compared to blackwater dark greywater usually contains less nutrients and breaks down much more rapidly in the environment Dark greywater is thus unlikely to cause severe pollution Adapting natural processes to human technology needs has resulted in such treatment processes as phytoremediation rock reed filter systems greywater systems blackwater systems biological treatment areas and constructed wetlands The reuse of wastewater on planted areas is nothing new to agrarian cultures it is documented that English and German farmers used wastewater as fertilizer as early as the 16th century Early Greeks did the same as did people in many Asian countries even before the days of Plato Greywater contributes 50 80 of the average total volume of water used in the home In many areas of the world that are facing severe water shortages greywater is an attractive alternative for reuse outdoors to water ornamental planting beds or lawns Greywater is a valuable on site resource which conserves precious drinking water reduces the load on wastewater disposal systems recharges dwindling groundwater supplies enhances plant growth and reuses vital nutrients Reusing greywater for garden irrigation should be encouraged in both urban and rural households 2 3 One of the main drawbacks of dark greywater for biological treatment units is the limitation on major nutrients like nitrogen and phosphate In the present investigation the raw dark greywater had a COD N P ratio of 100 1 82 0 76 while the preferred ratio for biological oxidation is 100 5 1 The observed nutrientdeficiency confirmed earlier research which found COD N P ratios of 100 1 64 1 284 and 168 0 8 2 4 5 In general every organism must find in its environment all of the substances required for energy generation and cellular biosynthesis The chemicals and elements of this environment that are utilized for bacterial growth Correspondence to Desa Ahmad Department of Biological Agricultural Engineering Faculty of Engineering University Putra Malaysia 43400 UPM Serdang Selangor Malaysia E mail desa eng upm edu my 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 00 Influence of COD N P ratio on greywater treatment are referred to as nutrients Carbon nitrogen and phosphate are considered to be the major nutrients On average carbon accounts for 50 of the dry weight of cellular material and it is the main constituent Nitrogen accounts for 14 of the dry weight and it is a constituent of aminoacids nucleic acids nucleotides and coenzymes Phosphorus accounts for 3 of dry weight and is found in nucleic acids nucleotides phospholipids and teichoic acids 6 The concept of recycling greywater in toilet flushing was also investigated after subjecting it to biological treatment and chlorination 7 filtration sedimentation and disinfection using hypochlorite 8 Lazarova et al 9 summarized the water quality of reclaimed urban water with reference to its application in toilet flushing Jeppesen10 stated that even though greywater is presumed to be free from fecal contamination when mixed with wash room wastewater there is a greater possibility of the presence of fecal coliform The diurnal variation in domestic wastewater volume and its quality was investigated by Almeida et al 1999 11 and Butler et al 1995 12 The characteristics of greywater were investigated by Palmquist and Hanaeus 2005 6 while Eriksson et al 2002 13 reviewed the greywater characteristics originating from different sources The effect of storage on untreated greywater was investigated by Dixon et al 1999 14 Elke et al 2003 15 highlighted the potential of greywater treatment and its reuse in rural areas with respect to treatment method and operational cost The biological treatment of greywater has been investigated using a sequencing batch reactor and microfiltration process 16 rotating biological contactor RBC and fluidized bed reactor 17 RBC and membrane bioreactor MBR 18 and membrane bioreactor and UV disinfection system
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