REUSE OF GRAYWATER FOR LANDSCAPE CULTURE

Abstract

Wastewater whether municipal or industrial needs to be treated before they could be feasibly used. Treatment means that wastewater undergoes a group of physical, chemical and biological processes. This processing is essential for both public health and environmentalprotection.In this work a lab scale system of Rotating Biological Contactor (RBC) was used for treating gray water collecting from a household facility which diverts water from the bath, shower and hand basin of a residencelocated at El- Adl St. EL-Marg city(ش العدل, ضاحية المرج), west of Cairo to be used in irrigating some ornamental plants i.e Epipremnum aureum and SyngoniumPodophyllum used in landscape culture. The RBC unit was modified with a provision to vary the speed (rpm) of rotating discs, Hydraulic Retention Time (HRT) and the disc surface area. The RBC unit had four different rotating speeds 2, 3, 4 and 5 rpm,six different hydraulic retention times 15, 30, 45, 60, 75, 90 min, and three different disc surface area 48×102, 64×102 and 80×102 cm2. The results indicated that the rotational speed of 4 rpm yielded better percent removal of COD at 72.5%. Hydraulic retention time 90 min yielded better percent removal of COD at 74.28%. Disc surface areas of 80×102 cm2 yielded better percent removal of COD at 76.47%.In addition Escherchia coli (E.coli) decreased from 4.2×103 CFU/100ml to be 3.8×102 CFU/100ml with removal efficiency 90.9%.Results also indicated a sharp decrease of the soil heavy metals (lead, copper and zinc) for treated gray water treatment. From the obtainedresults the amount of removed COD per unit volume of gray water (R)was affected with HRT (min) and Reynolds number (Re) where, Re is function with speed (V),amount of COD in raw gray water (C), flow rate (Q) and discs surface diameter (d)in a functional relationship. R/c= f (Re,(HRT . Q)/d^3 ). After achieving the optimum conditions, a greenhouse experiment was set up to examine the effects of treated gray water irrigation in comparison with raw gray water and fresh water on the vegetative growth of potted Epipremnum aureum and Syngonium podophyllumplants. These plants were cultivated in a medium consists of peat moss and sand (1:2).Results showed no significance was detected on all the growth measurementsconcerning the effect of treated gray water in comparison with the other two irrigation sources. However, the plants irrigated with raw gray waterdemonstrated best growth and good appearance (color and turgidity). It was noticeable also that the peat moss existed in the cultivated medium played a very good role for pollutants removal from the raw gray water.It was concluded that the Rotating Biological contactor (RBC) has a high performance in the removal of dissolved pollutants with less energy and it is more suitable for heavily polluted wastewater. Thus, it was recommended that raw gray wastewater must be analyzed before applying any treatment just to pick out the best and effective methodology suitable for the irrigation purpose.

Key words: Gray water – Rotating Biological Contactor (RBC) – COD – BOD – E. coli - Epipremnum aureum and Syngonium podophyllumplants