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Roughing filter can be consider as major pre-treatment process in waste water by reducing influent turbidity and suspended solids to a level that is effective for operation, meanwhile, roughing filter presents a promoting method for improving raw water quality without using any chemical. This research is aimed at improving Palm oil mill effluents (POME) using limestone roughing filter to remove Turbidity, Suspended Solids, Color, Ammonia Nitrogen, and COD. To reach this aim, tow different batches experiment include different size of limestone filter media and 3 various flow rates. Experiments have been conducted under various sizes of limestone in tow category of small and large size in 3, 6 and 12-20 mm sizes respectively, meanwhile range of 20, 50 and 100 ml/min flow rate was adopted in these experiments. Result indicated that removal efficient depended on size of filter media and applied flow rate. Turbidity, suspended solids, COD, Color, Ammonia Nitrogen removal was between52%, 62%37&, 26%55%. Removal efficiency was found to increase with slower flow rate and smallest size of media.
Keywords: Roughing filters; Pretreatment; Palm oil mill effluent (POME); Limestone;
Oil palm is known as the most compatible harvest product of both neighbor countries Malaysia and Indonesia(Latif Ahmad et al., 2003). Following steps have to be carried out in order to extract the palm oil from the fruit of (Elaeis guineensis) as sterilization, stripping, digestion, pressing, classification, purification, and vacuum drying. Extracting the Oil palm from the fruit, large amount of water almost 1.5 have to be consumed for every tone of fresh fruit bunch (FFB) however half will transfer to as palm oil mill effluent (POME). not only this material is known extremely polluting, Releasing POME in a single average-sized palm oil mill of 30 t/h FFB processing capacity, equal to 300,000 persons pollution is being produced (Zhang et al., 2008).This liquid in raw case is known as a thick brownish and is currently being released at the temperature within 80 to 90°. Palm oil mill effluent (POME) is a colloidal suspension of 95-96% water and 4-5% total solids, including 2-4% suspended solids, with a biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of 26.3 and 65.5 g/l, respectively. POME usually has a pH of 4-5 and contains appreciable amounts of nutrients for granulation (Ahmad et al., 2011). With the rapid expansion of the palm oil industry and the public's increased awareness of environmental pollution, the industry is obliged both socially and aesthetically to treat its effluent before discharging it so in 1977, the Malaysian Government proposed and legalized standards for POME discharge into watercourses (Oswal et al., 2002).Since then, palm oil mills are required to treat their POME prior to discharging it into streams and rivers. The parameter limits for POME discharge into watercourses in Malaysia are summarized in Table 1
Table 1. Parameter limits for POME discharge into water sources in Malaysia (Wu et al., 2010)
There is an urgent need to find a compromising way that will enable the balance between the environmental protection and sustainable reuse of the nutrient sources found in the POME. The current treatment system, which is based mainly on biological treatments of anaerobic and aerobic systems, is quite inefficient and this unfortunately leads to the environmental pollution issues (Wu et al., 2007). Roughing filters are primarily used to separate fine solids from the water that are only partly or not retained at all by stilling basin or sedimentation tanks. Roughing filters mainly acts as physical filters and reduce the solid mass. However, the large filter surface area available for sedimentation and relatively small filtration rates also supports adsorption as well as chemical and biological processes. Therefore, besides solid matter separation, roughing filters also partly improve the bacteriological water quality and, to a minor extent, change some other water quality parameters such as color or amount of dissolved organic matter (Nkwonta and Ochieng, 2009). The depth of the filter bed, maximizing the capacity of the filter to store removed solids. Particle removal efficiency in roughing filters is dependent on filter design, particulate, and water quality parameters (Nkwonta and Ochieng, 2010). Roughing filters are long troughs open to the atmosphere with a series of flow-through different sizes of gravel. The gravel often consists of crushed river rock media from a 20-mm average diameter to a 4-mm average diameter, and common flows range from 0.3 to 1.5 m/h of horizontal filter area (Rooklidge et al., 2002).In this research, limestone was used as a filter media because it is easily available and considerably cheaper also it could be used as filter media waste water treatment plants. It's composed of an accurate and closely screened aggregate which provided a surface for bacteria growth to enhance its purification process(Chen et al., 2007).
2. Materials and methods
2.1. Wastewater sampling and analysis
POME and palm oil sludge were obtained from the United Palm Oil Mill Sdn. Bhd, Nibong Tebal, Pulau Pinang, is chosen for the case study. The pounding POME treatment system has been employed to treat wastewater. Before start the sampling works, the location of the sampling point was decided by performed water quality tests on the samples from several ponds such as anaerobic, aerobic and polishing ponds. In this study, the POME samples were selected from polishing pond. This study involves two main methods which are field measurement and laboratory experiments. Field measurement includes test for Dissolved Oxygen (DO), pH and temperature by using DO meter, whilst laboratory experiments involve tests for Biochemical Chemical Oxygen Demand (COD), and Suspended Solids (SS), Color, turbidity, and Ammonia Nitrogen). All tests were conducted in accordance with the standard methods for the examination of water and wastewater(APHA, 2005). The typical characteristics of raw POME were shown in table 2
Table 2. Characteristics of row POME
Natural limestone media were used in this study provided from Perak. Prior to the experiment, the limestone was crushed of the three media size small size (3-6) and large size (12-20) their passed through No. 20 sieves, and then it was washed with water and dried. Local ordinary commercial limestone was used as sample whose chemical compositions are given in Table
Table characteristics of limestone
2.3. Batch study
In this study, horizontal roughing filters was selected as the pretreatment .The laboratory filter made by special perplexes material with 750mm length and 200mm height that was filled using media in various sizes (Figure1). The experiment was carried out at the environmental laboratory 2, School of Civil Engineering. Three type of batches was considered in this study as follow where the first batches has deployed the small sizes of lime stone in range of (3-6mm) and in the second batch, large sizes of limestone in range of 12-20 is adopted to filter the POME meanwhile range of 20, 50 and 100 ml/min flow rate was adopted in these experiments. Each experiment was run during 7 day. Both untreated and treat water samples were taken at different flow rates. Upon completion of the first batch of the experiment, the filter media was removed and tank was cleaned to prepare for the next batches. The removal was calculated as follows:
Where and indicated untreated water and treated water concentration respectively.
Figure 1. Schematic of laboratory-scale roughing filter.
The results adopted of horizontal flow limestone roughing filter treating wastewater from polishing pond of POME at different filtration rates showed that when the filter was run at lower flow rates the removal efficiencies had decreased. Conversely, when the flow rate was increased, removal efficiencies had decrease. Subsequently, it was observed that the performance of the roughing filter using limestone has been effective in reduction of turbidity, suspended solid, chemical oxygen demand, color and ammonia nitrogen, where the removal was between52%, 62%37&, 26%55% the maximum removing achieved in small sized and large size of media gave the least removal efficiency . Thus the role of limestone in filtration, particularly in roughing filter has shown a promising result to be used for future undertaking for water and waste water treatment. The roughing filtration using limestone as a filter media for waste water treatment is a simple process and the cost will be reduced in area where limestone is abundant. Therefore, this technique could be used a alternative to other forms of filtration.