**2.2 Characteristics of POME**

The POME from different mills would have different characteristics due to different oil extraction technique, FFB quality, climate, condition of palm oil

*Performance of Chitosan as Natural Coagulant in Oil Palm Mill Effluent Treatment DOI: http://dx.doi.org/10.5772/intechopen.94330*

processing and mill requirement on POME discharge limit [6]. POME is a mixture of water (up to 95%), oil and fine suspended solids [7]. The suspended solid (TSS) is the vegetative matter such as cell walls, organelles, short fibers, water-soluble carbohydrates (glucose, reducing sugar and pectin), nitrogenous compound (protein and amino acid), free organic acid, lipids and also combined small organic and mineral constituents [8]. POME is considered as non-toxic waste as the palm oil mills usually do not use any harmful chemical in the entire milling process [1]. The dark color of POME is usually caused by the decomposition of lignocellulosic materials; which produces lignin, tannin, humic acids, carotene and other organic matter that are recalcitrant to conventional treatment [9]. These suspended solids will eventually contribute to the high BOD of POME [1].

In term of organic content, based on the biochemical oxygen demand (BOD), raw POME has an average BOD of 25,000 mg/L. Raw POME is highly acidic. Biodegradability of effluent can be determined from the BOD/COD ratio. COD stands for chemical oxygen demand. BOD/COD ratio indicates the fraction of chemically oxidized organics which is eligible for biological degradation. In East Malaysia, the POME discharged when the BOD is less than 50 mg/L as required by Department of Environment (DOE). The pollution load of POME generated in a palm oil mill in a day can be calculated based on the following Eq. (1) and (2):

$$\text{Pollution Load}, \frac{\text{kg}}{\text{d}} = \frac{\text{POME Flow Rate}, \frac{\text{m}^3}{\text{d}} \ge \text{Concentration}, \text{mg}/\text{L}}{1000} \tag{1}$$

$$\text{POME Flow Rate}, \frac{\text{m}^3}{\text{d}} = \text{Process capacity} \frac{\text{ton FFB}}{\text{h}} \times \text{Process Efficiency}, 96$$

$$\times \text{Operating Hours,} \frac{\text{h}}{\text{d}} \times \text{POME generated}, \frac{\text{m}^3}{\text{ton}} \tag{2}$$

#### **2.3 Biochemical oxygen demand (BOD)**

Biochemical oxygen demand (BOD) is the measure of the amount of oxygen that bacteria will consume during the decomposition of organic matter content under aerobic conditions. BOD test should be carried out according to APHA Standard Method 5510B [10]. BOD is determined by incubating a sealed sample of water for five days and measuring the loss of oxygen from the beginning to the


**Table 2.**

*Characteristic of different sources of wastewater [1].*

end of the test. The samples are usually diluted before the incubation because the bacteria could deplete all of the oxygen in the bottle before the test is complete [11]. It is essential to determine the sample size and dilution ratio before the BOD test, as this will ensure valid BOD results. The pH value of the samples should be in the range of 6.0–8.0, as alkalinity or acidity of samples can prevent bacteria from growing during the BOD test. pH can adjust by adding sodium hydroxide (NaOH) and sulfuric acid (H2SO4) [10]. When the test carries out in this way, the BOD usually abbreviated as BOD5. BOD is a severe problem in natural waters because the dissolved oxygen (DO) of the water can be stressed by BOD oxidation [12].

#### **2.4 Chemical oxygen demand (COD)**

Chemical oxygen demand is a measure of the amount of oxygen required to oxidize all organic material into carbon dioxide and water. COD values usually are higher than BOD values, but COD measurements can be obtained in a few hours while BOD measurements will take around five days [11]. Samples heated for 2 hours with sulfuric acid and strong oxidizing agent potassium dichromate. The reduction reaction is shown in Eq. (3).

$$\text{\textbullet Cl'} \star \text{Cr}\_2\text{O}\_7^{2-} \star \text{14H'} \rightarrow \text{\textbullet Cl}\_2 \star \text{2Cr}^{3+} \star \text{7H}\_2\text{O} \tag{3}$$

The amount of Cr3+ produced is measured at wavelengths and reflected in mg/L of COD.

#### **2.5 Total suspended solids (TSS)**

Total suspended solids are a measure of suspended matter contained in the wastewater. Suspended solids contain BOD and can impair water quality by adding turbidity and reducing esthetics. Discharges of SS also caused deposits that developed at the bottom of waterways. In the laboratory, standard filtration and drying method used to measure SS, where the increase of weight of a container/filter is measured, for a known volume of wastewater filtered [12]. The TSS before and after the experiment measured according to Standard Methods Section 2540 D, and total solids dried from 103–105°C. The treated and the untreated POME samples were evaporated in a weighed dish and dried to a constant weight in an oven from 103–105°C. The increase in weight over the empty dish represents the total solids. TSS calculation is shown in Eq. (4).

$$\text{TSS} \left( \frac{\text{mg}}{\text{L}} \right) = \frac{\left( \text{Weight of dried residue} + \text{disk} - \text{weight of disk} \right) \text{mg} \ge 1000}{\text{sample volume}, \text{ml}} \tag{4}$$

#### **2.6 Conventional method in POME treatment**

The natural chemical properties of the POME make it easily treated by a biological approach. Currently, there are three biological processes employed in the palm oil industry which are anaerobic, facultative anaerobic, and aerobic treatments. The anaerobic treatment is the major part which is removing pollutant (BOD). It can remove BOD up to 95% [13]. There are four main stages which are hydrolytic, acidogenic, acetogenesis and methanogenic. The hydrolysis process begins with bacteria of insoluble organic polymers (carbohydrate) and complex organic compound (protein and lipid) to make them available for other bacteria. Hydrolytic microorganisms will secrete extracellular enzymes for hydrolysis. This process will convert organics into simpler molecule such as amino acids, glycerol, triglycerides,

#### *Performance of Chitosan as Natural Coagulant in Oil Palm Mill Effluent Treatment DOI: http://dx.doi.org/10.5772/intechopen.94330*

sugar and fatty acids. Meanwhile, in acidogenesis process, the hydrolyzed or soluble products from the first stage are further broken down by acidogen into simpler organic compound such as volatile fatty acid (VFA), ammonia, carbon dioxide, hydrogen and hydrogen sulfide. In the acetogenesis process, the simple molecule from the previous stage is further digested by acetogens to produce carbon dioxide, hydrogen and acetic acid. For the methanogenesis process, the acetic acid, hydrogen and VFA are converted to methane, carbon dioxide and water by methanogens.

The ponding system is a combination of a series anaerobic, facultative, and algae (aerobic) ponds, as shown in **Figures 3** and **4**. Ponding system primarily anaerobic and facultative ponds require less energy as it does not need mechanical mixing, operation control or monitoring. The major drawback of the ponding system is a large area of land is needed to accommodate a series of ponds to achieve the discharge limit [13]. In constructing the ponds, depth is the primary consideration for different types of ponds. However, the optimum depth for the anaerobic pond is 5-7 m, the facultative anaerobic pond is 1–1.5 m and aerobic pond is 0.5-1 m. The sufficient hydraulic retention time (HRT) of anaerobic, facultative anaerobic and aerobic ponds are 45, 20 and 14 days, respectively [13]. The problems arise from the ponding system is the formation of scum. Scum form when the bubbles rise to the surface together with the fine suspended solids. It is caused by the presence of oil and grease in the POME. Another drawback of the ponding system is the solid

**Figure 3.** *Series of ponds for POME treatment.*

**Figure 4.**

*Typical configuration for ponding treatment system for POME [14].*

sludge accumulates at the bottom of the ponds. It will affect the effectiveness of the pond as it decreases the volumetric capacity and hydraulics retention time (HRT) [13]. Therefore, de-sludging is required when the sludge is more than one-third of the pond. About 85% of the palm oil mills that POME in Malaysia adopted ponding system because it is inexpensive, low capital, simple and easy to handle [14]. The palm oil industry is widely favored to the ponding system as only clay lining of ponds is needed and can be constructed easily by excavating hence low marginal cost [4].

The combination of open digester and ponding system is another type of conventional POME treatment system that combines an open digester tank with a series of ponds. **Figure 5** shows a typical open digester tank. Digester tank may build with various volumetric capacities ranging from 600 until 3600 m3 . In this treatment method, digester has the same function as the anaerobic pond. It carries out the anaerobic digestion. The output of the POME from the digester will then enter facultative anaerobic ponds and then algae (aerobic) ponds. The digester can decrease the BOD in a shorter time than the pond. The HRT for digester is only 20–25 days which is a lot shorter than anaerobic ponding system. Although it is proven that the digester is more effective than anaerobic ponds, it brings some drawback to the operator. The disadvantages of digester include scum formation on the top, sludge accumulation at the bottom and the corrosion of the steel structure of the digesters due to prolonged exposure to hydrogen sulfide. There are incidents which reported that the digester burst and collapsed [13].

**Figure 5.** *Typical open digester tank.*

*Performance of Chitosan as Natural Coagulant in Oil Palm Mill Effluent Treatment DOI: http://dx.doi.org/10.5772/intechopen.94330*

**Figure 6.** *Surface aerator for POME ponds.*

Extended aeration is to complement the previous conventional treatment system, which shown in **Figure 6**. In this treatment method, mechanical surface aerators are introduced at the aerobic ponds to supply more oxygen to the ponds. It can reduce the BOD in POME effectively by aerobic processes. Usually, the surface aerators are installed at the end of the ponds before discharging the POME. This treatment method is useful only used when the land area is a constraint and does not permit extensive wastewater treatment [13].
