Removal of Important Parameter from Car Wash Wastewater - A Review

Abstract. Huge quantity of water consumed per car and the various chemical agents used in car wash activities discharged the untreated effluents into stormwater system and eventually ending up in our lakes, rivers and oceans [1]. The accumulated sediments from vehicle wash contain contaminants that reach concentrations where the sludge is considered as a controlled or hazardous waste including of metals, elevated levels of oil and grease, and the unacceptable levels of acidity or alkalinity [2]. This paper provides a comprehensive review of car wash wastewater data analyzes regarding the wastewater discharges, as well as contaminant levels of car wash activities. Besides, the further extensive research on treatments used for the car wash industry for pollutant removal routes including the removal effeciency of pollutants has also been highlighted. The expansion of the review on the influence of the treatment indicates that, the effeciency on removal pollutants depends on the treatment used. Overall, the review illustrates the necessity of a profound knowledge on the car wash wastewater with an extensive lists of common treatment of car wash wastewater in providing the alternative way for on-site treatment for car wash outlet in treating the effluent before discharging into water bodies. Hence, decreases the pollution governing environmental, operational parameters, and the treatment performances of low cost system in treating the car wash wastewater.


Introduction
In this worldwide, about 20 million hectares of land are occupied with treated and untreated wastewater use. Malaysia has their own environmental quality regulations, but seldom enforced to the car wash industry [3]. The car wash discharge system cannot mix with the stormwater system, where it can contribute to the permeation of other pollutants towards the aquatic animals [9,17]. A car wash is defined as a non-domestic installation for external cleaning of cars, offering consumers a practical way to wash dirts from their automobiles [3,4]. The Environmental Pollution Agency rose awareness of the following list from vehicle washes such as detergents, heavy metals, oil, grease, polycylic aromatic hydrocarbons (PAH's) and volatile organic compounds (VOC's) [3,12,14]. Oil and grease contain toxic substances which are carcinogenic to human beings whereas, the accumulation of heavy metals concentrations reducing microbial activity, lead to the inhibition of chlorophyll synthesis which hazard to the ecosystem [12,18,19]. Moreover, the synthetic anionic surfactants, commonly linear alkyl sulphate (LAS) and sodium dodecyl sulphate (SDS) components from detergent of car wash activities are very slow to biodegrade into the environment, lowering the oxygenation potential and hence, kills the waterborne organisms [8]. Hence, the concentration and severity each element should be assessed and considered in treating the pollutants. In this review, an extensive lists of treatment for car wash wastewater from conventional methods has been compiled and discussed. The efficiency of each system in removing pollutants were analyzed and compared.

2.1
Car wash wastewater treatment

Ultrafiltration (UF) and nanofiltration (NF) membrane
Generally, the membrane technologies commonly used in wastewater treatment, including of UF and NF membrane [12]. With the aid of the UF membrane, the biodegradable organics, colloids and some viruses can be removed as presented in Table 1. UF membrane and NF membrane have different performances in treating wastewater [10,13,15,18]. The oil emulsion are the main pollutant observed in car wash wastewater, commonly by the detection of PAH's in lubricant oils. A study reported the oil emulsion was not absorbed directly to the NF membrane due to the negative charge repulsion between anionic emulsion and membrane surface, where the NF membrane removing 98% of pollutants of total organic carbon compared to UF membrane [15]. The UF membrane is ineffective in removing conductivity and total dissolved solids removal, because the membrane has flux deterioration and low flux recovery rate [14]. Apart from using the UF and NF membrane itself, the performance of hybrid system combining the bio-carriers and non-woven membrane filtration was explored. Rather than the UF membrane, the non-woven material of the membrane separating the suspended solid at lower operating pressure and reasonable cost. The bio-carriers have large porous structures of surfaces allowed it to trap the attached growth microorganisms and then degrading the biodegradable matter, and removing the organic removal of car wash wastewater [13].

Oil separator
The oil separator was designed to ensure the removal of all light oils escaped from the oil skimmer in the settling tank. In this study, the authors suggested the treated water from the study can be used for wash and pre rinse for the car washes [2]. Besides, the conventional oil separator has less of specific standards recommended for the design of gravity separators for car wash stations. Based on the performance of the gravity oil separators observed in the car wash industries, the authors concluded the system does not allow producing an effluent that complies with the discharge limits established in the sewage system. The removal of oil and grease (O&G), total suspended solid (TSS), volatile suspended solid (VSS), total dissolved solid (TDS), and chemical oxygen demand (COD) exhibited better results of removal by using gravity oil separators. However, the results of chemical oxygen demand and total suspended solid were not followed the sewer discharge standards [8].

Chemical oxidation
The chemical oxidation including process of aeration for oil water separation, alum treatment for pollutant removal with aid of hydrogen peroxide. The aeration responsible to separate the oil and water by trapping the oil by the air bubbles carrying oxygen. Total chemical oxygen demand reduction after going through the overall processes was 93%. The increase dosage of alum alone for the treatment does not meet the desired discharge standard. The aid of hydrogen peroxide creates positively charged and polynuclear species, resulting charged compounds react with colloids attained with negative ions present in the wastewater. The gravity force helps in removing of suspended solids and chemical oxygen demand. Moreover, the alum act as a coagulant whereas the hydrogen peroxide reducing the concentration of chemical oxygen demand from car wash wastewater. The further treatment by waste hydrogen peroxide were done subsequently after the aeration and addition of alum processes. The present study has potential to reduce the cost of water treatment and requires less space without any pH control [3].

Flocculation column flotation (FCF), sand filtration (SF) and final chlorination (FC)
Flocculation allows the removal of organic matters and colours of wastewater. However, the treatment should be furthered studied with the other processes, depends on the proper selection of flocculant and proper designed of system to improve the operations [16]. Treatment of car wash wastewater by flocculation column flotation experimented in Brazil. However, the results obtained were high for turbidity and colour due to the existence of bubbles, the presence low surface tension and oil and grease which yielding the light flocs [19]. Another study in 2013 have combined a bench study of FCF and SF followed by a FC for car wash wastewater treatment. The SF process helps in removing the pathogenic microorganisms from car wash wastewater and the process of chlorination inhibit the growth of E. Coli. The last stage of treatment, final chlorination helps in removing the pathogens and other microorganisms that may have passed by SF. During the process, the chlorine disinfection deactivated the microorganism lives resulting death of different mechanisms. As the results, the coupled system of the treatment effective with removal of E. Coli, TSS, turbidity, TOC were 99%, 91%, 91% and 95% respectively [21].

Hydrophilic and hydrophobic membrane
The hydrophilic and hydrophobic membrane has a high water permeability with different surfactants and the membrane fouling have been studied. The results show that the hydrophilic membrane was more efficient in removing different type of surfactants compared with hydrophobic membrane. Hydrophilic membrane was not damaged after undergoing the treatment of car washes. Moreover, there was no chemical needed to enhance the membrane flux of the membrane. The authors have concluded that the nanofiltration membrane can also be used for recycling wastewater [4].

Conclusions
There was lack information regarding the treatment used for car wash wastewater treatment system. In spite of using conventional methods and simple treatment strategies for car wash wastewater treatment system, a wide range of any low cost potential wastewater treatment should have been investigated and studied. Some of the treatment system was found to be quite satisfactory in removing pollutants. However, there is a strong need to conduct extensive research due to the reuse and reclaiming of car wash wastewater as other potential to reduce scarcity in worldwide rather than disposed it. If it is possible in developing other low cost and simple treatment differ from the treatment that have been reviewed, then these treatments may offer many advantages and commercially attracting consumers and developers of car wash stations, and hence contribute to the way of minimizing pollutants of car wash wastewater.