Reuse of car wash wastewater by chemical coagulation and membrane bioreactor treatment processes
Introduction
Water recycling provides a great opportunity to conserve one of our natural resources that is essential for the survival of mankind. Reducing wastewater and being able to reuse it as resource is critical in light of long term droughts. There are currently more than 17.6 million motor vehicles registered in Australia (Australian Bureau of Statistics, 2014). All these vehicles need to be washed frequently, either by a household car wash or by a commercial car wash service. The latter is a recent industry which is gaining popularity due to its positive environmental impacts, comparing it with the household car wash method. Car wash facilities usually have two types of services (automatic and self-serve wash). Generally, 200 L of water are used in automatic wash every time a car is washed; and from 40 to 50 kL in a self-serve wash. Thus, car wash requires a big volume of water and also it generates a significant volume of wastewater containing various types of pollutants. Most of the time, the car wash wastewater is discharged into sewer systems without any treatment. For example, up to 10,000 L of wastewater a day can be generated at a commercial car wash station in Geelong, Australia. This equates to in excess of 3.5 million litres per annum of wastewater which is disposed of rather than recycled. If this is extrapolated across the more than 10,000 car wash facilities in Australia, it would represent over 35 billion litres of wastewater per annum. The current water price for businesses supplied by Barwon Water in the Geelong region is approximately AUD$2.21 per kilolitre. With a total volume of thirty-five billion litres of wastewater being produced by car washes Australia wide each year, the total value of the wastewater disposed of through the sewerage system is around AUD$77.35 million.
Chemical, biological and membrane processes have been widely used in treating various kinds of industrial and municipal wastewater. Sabur et al. (2012) used coagulation processes for treating a textile wastewater and found that the removal efficiency of COD, total dissolved solids and turbidity was 90%, 74% and 93%, respectively. Amuda and Amoo (2007) reported that coagulation was capable of removing 73%, 95% and 97% of chemical oxygen demand (COD), total phosphorus (TP) and total suspended solids (TSS), respectively, from beverage industrial wastewater. Moreover, membrane bioreactor (MBR) was highly effective in reducing the contaminants from industrial wastewater. Hosseinzadeh et al. (2013) found that MBR led to a removal of 75%, 98% and 74% removal of COD, TSS and total nitrogen (TN), respectively, from industrial town wastewater. Cheng et al. (2015) studied the effect of MBR treatment for antibiotic wastewater treatment and found that MBR could remove 92.5% of BOD, 96% of COD, 81.5% of suspended solids and more than 99.9% of selected antibiotics such as imipenem and cilastatin. Another study by Friha et al. (2014) found that aerobic submerged MBR could effectively treat the cosmetic wastewater with a removal of 98.13% of anionic surfactant and 83.73% of COD. However, only a few studies have investigated car wash wastewater treatment with the aim of producing reusable effluent. The car wash wastewater was extremely murky and the presence of suspended solids was noticeable. Rubio and Zaneti (2009) found that flocculation column-flotation treatment could effectively reduce the turbidity and colour (>90% and 75%, respectively) from cash wash wastewater.
Lau et al. (2013) found that ultrafiltration and nanofiltration for car wash water reclamation effectively reduced COD, TDS and turbidity. Kiran et al. (2015) compared the efficiency of modified polyethersulfone and cellulose acetate membranes in the treatment of carwash effluent using ultrafiltration and found that the modified membranes performed better at removing COD, turbidity and maintaining stable flux than commercial polyethersulfone (PES) membrane. However, it is important to consider the costs of implementation, operation and maintenance along with the efficiency of the treatment process. Compared to conventional treatment technologies, MBR appears to be suitable for the removal of all types of contaminants present in cash wash effluent since it has the ability to meet high permeate quality and small space requirement. Small footprint for space is required due to its limited availability in a car wash station and high effluent quality is required in order to reuse in washing cars. The objective of this research was to investigate the impact of different treatment processes including MBR, coagulation and ozonation in treating car wash wastewater.
Section snippets
Sample collection
The feed water was collected from Grovedale car wash in Geelong, Australia. Car wash wastewater pre-treated in an oil and grease separator was employed for this study. Samples were stored at 4 °C and brought back to room temperature (22 ± 2 °C) prior to all tests.
MBR setup
The schematic of the laboratory-scale MBR experimental setup is shown in Fig. 1. The system was constructed with five tanks including a 10 L feed tank, two 6 L anoxic reactors (AR1 and AR2), a 10 L aerobic membrane bioreactor (AMBR)
Performance of coagulation and ozonation
The characteristics of the car wash effluent before and after coagulation with Alum and PACl are shown in Table 1 (The values are average of two readings with a standard deviation less than ± 1%). The concentration of turbidity and suspended solids of the raw car wash wastewater was 1000 NTU and 4.2 mg/L, respectively. Etchepare et al. (2014) and Lau et al. (2013) reported that the concentration of turbidity of car wash wastewater was 229 and 68.9 to 62.8 NTU, respectively. Clearly, the level
Conclusions
This study demonstrated the efficiency of the coagulation, ozonation and MBR in removing both solids and chemical contaminants from a car wash wastewater sample. Coagulants, alum and PACl, reduced all types of contaminants from car wash wastewater. Ozonation was an effective method to remove particular contaminants of car wash wastewater compared to coagulation. The quality of the permeate produced by the MBR was extremely high. It is anticipated that the outcomes of this study from MBR may
Acknowledgements
The authors are grateful to the owner of Grovedale Car Wash, Mr. Joe Pongrac for initiating this research by providing background to problems faced due to carwash wastewater and supplying wastewater samples to conduct this research.
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