**Ultrasonic Membrane Anaerobic System (UMAS) for Palm Oil Mill Effluent (POME) Treatment**

N.H. Abdurahman, N.H. Azhari and Y.M. Rosli

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/54459

## **1. Introduction**

[86] Parawira, W, Murto, M, Zvauya, R, & Mattiasson, B. (2006). Comparative perform‐ ance of a UASB reactor and an anaerobic packed-bed reactor when treating potato

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Palm oil mill effluent (POME) is an important source of inland water pollution when released into local rivers or lakes without treatment. The production of palm oil, however, results in the generation of large quantities of polluted wastewater commonly referred as palm oil mill efflu‐ ent (POME). In the process of palm oil milling, POME is generated through sterilization of fresh oil palm fruit bunches, clarification of palm oil and effluent from hydro-cyclone operations [1]. POME is a viscous brown liquid with fine suspended solids at pH ranging between 4 and 5 [2]. In general appearance, palm oil mill effluent (POME) is a yellowish acidic wastewater with fair‐ ly high polluting properties, with average of 25,000 mg/l biochemical oxygen demand (BOD), 55,250 mg/l chemical oxygen demand (COD) and 19,610 mg/l suspended solid (SS). This highly polluting wastewater can cause several pollution problems. Anaerobic digestion is the most suitable method for the treatment of effluents containing high concentration of organic carbon such as POME [1]. Anaerobic digestion is defined as the engineered methanogenic anaerobic decomposition of organic matter. It involves different species of anaerobic microorganisms that degrade organic matter [3]. In the anaerobic process, the decomposition of organic and inorgan‐ ic substrate is carried out in the absence of molecular oxygen. The biological conversion of the organic substrate occurs in the mixtures of primary settled and biological sludge under anaero‐ bic condition followed by hydrolysis, acidogenesis and methanogenesis to convert the inter‐ mediate compounds into simpler end products as methane (CH4) and carbon dioxide (CO2) [4], [5], and [6]. Therefore, the anaerobic digestion process offers great potential for rapid disinte‐ gration of organic matter to produce biogas that can be used to generate electricity and save fos‐ sil energy [7]. The suggested anaerobic treatment processes for POME include anaerobic suspended growth processes, attached growth anaerobic processes (immobilized cell bioreac‐ tors, anaerobic fluidized bed reactors and anaerobic filters), anaerobic blanket processes (up-

© 2013 Abdurahman et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Abdurahman et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. licensee InTech. This is a paper distributed under the terms of the Creative Commons

flow anaerobic sludge blanket reactors and anaerobic baffled reactors), membrane separation anaerobic treatment processes and hybrid anaerobic treatment processes.

bic system (UMAS) which consists of a cross flow ultra-filtration membrane (CUF) apparatus, a centrifugal pump, and an anaerobic reactor. 25 KHz multi frequency ultrasonic transducers (to create high mechanical energy around the membrane to suspends the parti‐ cles) connected into the MAS system. The ultrasonic frequency is 25 KHz, with 6 units of permanent transducers and bonded to the two (2) sided of the tank chamber and connected to one (1) unit of 250 watts 25 KHz Crest's Genesis Generator. The UF membrane module had a molecular weight cut-off (MWCO) of 200,000, a tube diameter of 1.25 cm and an aver‐ age pore size of 0.1 µm. The length of each tube was 30 cm. The total effective area of the four membranes was 0.048 m². The maximum operating pressure on the membrane was 55 bars at 70 ºC, and the pH ranged from 2 to 12. The reactor was composed of a heavy duty reactor with an inner diameter of 25 cm and a total height of 250 cm. The operating pressure in this study was maintained between 2 and 4 bars by manipulating the gate valve at the

Ultrasonic Membrane Anaerobic System (UMAS) for Palm Oil Mill Effluent (POME) Treatment

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109

retentate line after the CUF unit.

**Figure 1.** Experimental set-up

Over the past 20 years, the technique available for the treatment of POME in Malaysia has been biological treatment, consisting of anaerobic, facultative and aerobic pond systems [8, 9]. Anae‐ robic digestion has been employed by most palm oil mills as their primary treatment of POME [10]. More than 85% of palm oil mills producers in Malaysia have adopted the ponding system for POME treatment [11] due to its low capital and operating costs, while the rest opted for open digesting tanks [12]. These methods are regarded as conventional POME treatment method whereby long retention times and large treatment areas are required. High-rate anaerobic bio‐ reactors have also been applied in laboratory-scaled POME treatment such as up-flow anaero‐ bic sludge blanket (UASB) reactor [13]; up-flow anaerobic filtration [14]; fluidized bed reactor [15, 16] and up-flow anaerobic sludge fixed-film (UASFF) reactor [2]. Anaerobic contact digest‐ er [12] and continuous stirred tank reactor (CSTR) have also been studied for POME treatment [17]. Other than anaerobic digestion, POME has also been treated using membrane technology [14, 18, 19], [20] and [21]. (POME's) chemical oxygen demand (COD) and biochemical oxygen demand (BOD) are very high; COD values greater than 80,000 mg/l and; pH values in the acidic range between (3.8 and 4.5) are frequently reported and the incomplete extraction of palm oil from the palm nut can increase COD values substantially. The effluent is non-toxic because no chemicals are added during the oil extraction process [22, 23, and 24]. (POME) is a brownish col‐ loidal suspension, characterised by high organic content, and high temperature (70-80 o C) [25]. Most commonly, palm oil mills have already suggested use of anaerobic digesters for the pri‐ mary treatment [26, 27]. The three widely used kinetic models considered in this study are shown in Table 1. The traditional ways for wastewater treatment from both economic (high cost ) and environmental (harmful) disadvantages, this paper aims to introduce a new design technique of ultrasonic-membrane anaerobic system (UMAS) in treating POME and producing methane and to determine the kinetic parameters of the process, based on three known models; Monod [28], Contois [29] and Chen and Hashimoto[30].


**Table 1.** Mathematical expressions of specifics substrate utilization rates for known kinetic models

## **2. Materials and methods**

Raw POME was treated by UMAS in a laboratory digester with an effective 200-litre vol‐ ume. Figs. 1&2 presents a schematic representation of the ultrasonicated-membrane anaero‐ bic system (UMAS) which consists of a cross flow ultra-filtration membrane (CUF) apparatus, a centrifugal pump, and an anaerobic reactor. 25 KHz multi frequency ultrasonic transducers (to create high mechanical energy around the membrane to suspends the parti‐ cles) connected into the MAS system. The ultrasonic frequency is 25 KHz, with 6 units of permanent transducers and bonded to the two (2) sided of the tank chamber and connected to one (1) unit of 250 watts 25 KHz Crest's Genesis Generator. The UF membrane module had a molecular weight cut-off (MWCO) of 200,000, a tube diameter of 1.25 cm and an aver‐ age pore size of 0.1 µm. The length of each tube was 30 cm. The total effective area of the four membranes was 0.048 m². The maximum operating pressure on the membrane was 55 bars at 70 ºC, and the pH ranged from 2 to 12. The reactor was composed of a heavy duty reactor with an inner diameter of 25 cm and a total height of 250 cm. The operating pressure in this study was maintained between 2 and 4 bars by manipulating the gate valve at the retentate line after the CUF unit.

**Figure 1.** Experimental set-up

flow anaerobic sludge blanket reactors and anaerobic baffled reactors), membrane separation

Over the past 20 years, the technique available for the treatment of POME in Malaysia has been biological treatment, consisting of anaerobic, facultative and aerobic pond systems [8, 9]. Anae‐ robic digestion has been employed by most palm oil mills as their primary treatment of POME [10]. More than 85% of palm oil mills producers in Malaysia have adopted the ponding system for POME treatment [11] due to its low capital and operating costs, while the rest opted for open digesting tanks [12]. These methods are regarded as conventional POME treatment method whereby long retention times and large treatment areas are required. High-rate anaerobic bio‐ reactors have also been applied in laboratory-scaled POME treatment such as up-flow anaero‐ bic sludge blanket (UASB) reactor [13]; up-flow anaerobic filtration [14]; fluidized bed reactor [15, 16] and up-flow anaerobic sludge fixed-film (UASFF) reactor [2]. Anaerobic contact digest‐ er [12] and continuous stirred tank reactor (CSTR) have also been studied for POME treatment [17]. Other than anaerobic digestion, POME has also been treated using membrane technology [14, 18, 19], [20] and [21]. (POME's) chemical oxygen demand (COD) and biochemical oxygen demand (BOD) are very high; COD values greater than 80,000 mg/l and; pH values in the acidic range between (3.8 and 4.5) are frequently reported and the incomplete extraction of palm oil from the palm nut can increase COD values substantially. The effluent is non-toxic because no chemicals are added during the oil extraction process [22, 23, and 24]. (POME) is a brownish col‐ loidal suspension, characterised by high organic content, and high temperature (70-80 o

Most commonly, palm oil mills have already suggested use of anaerobic digesters for the pri‐ mary treatment [26, 27]. The three widely used kinetic models considered in this study are shown in Table 1. The traditional ways for wastewater treatment from both economic (high cost ) and environmental (harmful) disadvantages, this paper aims to introduce a new design technique of ultrasonic-membrane anaerobic system (UMAS) in treating POME and producing methane and to determine the kinetic parameters of the process, based on three known models;

> 1 *<sup>U</sup>* <sup>=</sup> *Ks K* ( 1 *<sup>S</sup>* ) <sup>+</sup> <sup>1</sup> *<sup>k</sup>* [28]

<sup>μ</sup>max×*<sup>S</sup>* <sup>+</sup> *<sup>Y</sup>* (1 <sup>+</sup> *<sup>a</sup>*) μmax

<sup>μ</sup>max *<sup>S</sup>* <sup>+</sup> *<sup>Y</sup>* (1<sup>−</sup> *<sup>K</sup>*) <sup>μ</sup>max

[29]

[30]

1 *<sup>U</sup>* <sup>=</sup> *<sup>a</sup>*<sup>×</sup> *<sup>X</sup>*

1 *<sup>U</sup>* <sup>=</sup> *<sup>Y</sup> <sup>K</sup> So*

**Kinetic Model Equation 1 Equation 2**

**Table 1.** Mathematical expressions of specifics substrate utilization rates for known kinetic models

Raw POME was treated by UMAS in a laboratory digester with an effective 200-litre vol‐ ume. Figs. 1&2 presents a schematic representation of the ultrasonicated-membrane anaero‐

*<sup>U</sup>* <sup>=</sup> *<sup>k</sup> <sup>S</sup> ks* + *S*

*<sup>U</sup>* <sup>=</sup> *<sup>U</sup>*max×*<sup>S</sup> Y* (*B* × *X* + *S*)

*<sup>U</sup>* <sup>=</sup> <sup>μ</sup>max×*<sup>S</sup> Y K So* + (1− *K*) *S Y*

Monod [28], Contois [29] and Chen and Hashimoto[30].

Monod Contois Chen & Hashimoto

**2. Materials and methods**

C) [25].

anaerobic treatment processes and hybrid anaerobic treatment processes.

108 International Perspectives on Water Quality Management and Pollutant Control

**Steady State (SS) 1 2 3 4 5 6** COD feed, mg/L 67000 79000 82400 86000 90000 91400 COD permeate, mg/L 980 1940 1650 1980 2200 3000 Gas production (L/d) 280.5 357 377 395 470 540 Total gas yield, L/g COD/d 0.29 0.38 0.65 0.77 0.82 0.88 % Methane 79 75.5 70.2 71.8 70.6 68.5 Ch4 yield, l/g COD/d 0.29 0.32 0.50 0.54 0.56 0.59 MLSS, mg/L 12960 13880 15879 17700 20000 25600 MLVSS, mg/L 10091 10950 12624 14638 17000 22528 % VSS 77.86 78.89 79.50 82.7 0 85.00 88.00 HRT, d 480.3 76.40 20.3 8.78 7.36 5.40 SRT, d 860 320 132 32.6 14.56 10.6 OLR, kg COD/m3/d 0.5 1.5 3 5.5 8.5 9.5 SSUR, kg COD/kg VSS/d 0.185 0.262 0.266 0.274 0.315 0.321 SUR, kg COD/m3/d 0.0346 0.8454 3.3028 5.6657 7.7753 9.4528 Percent COD removal (MAS) **96.5 96.0 95.8 95.4 94.9 94.8** Percent COD removal (UMAS) **98.5 97.5 98.0 97.7 97.6 96.7**

Ultrasonic Membrane Anaerobic System (UMAS) for Palm Oil Mill Effluent (POME) Treatment

**Model Equation** *R* <sup>2</sup> (*%*)

*Ks* =498 *K* =0.350 μ*Max* =0.284

*B* =0.111 *uMax* =0.344 *a*=0.115 μ*Max* =0.377 *K* =0.519

*K* =0.006 *a*=0.006 μ*Max* =0.291 *K* =0.374

**Table 3.** Results of the application of three known substrate utilisation models

*U* <sup>−</sup><sup>1</sup> =2025 *S* <sup>−</sup><sup>1</sup> + 3.61

*U* <sup>−</sup><sup>1</sup> =0.306 *X S* <sup>−</sup><sup>1</sup> + 2.78

*<sup>U</sup>* <sup>−</sup><sup>1</sup> =0.0190 *So <sup>S</sup>* <sup>−</sup><sup>1</sup> <sup>+</sup> 3.77

98.9

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111

97.8

98.7

**Table 2.** Summary of results (SS: steady state)

Monod

Contois

Chen & Hashimoto

**Figure 2.** Schematic for Ultrasonicated membrane anaerobic system (UMAS)

## **2.1. Palm oil mill effluent**

Raw POME samples were collected from a palm oil mill in Kuantan-Malaysia. The wastewa‐ ter was stored in a cold room at 4o C prior to use. Samples analysed for chemical oxygen de‐ mand (COD), total suspended solids (TSS), pH, volatile suspended solids (VSS), substrate utilisation rate (SUR), and specific substrate utilisation rate (SSUR).

## **2.2. Bioreactor operation**

The ultrasonicated membrane anaerobic system, UMAS Performance was evaluated under six different inflow conditions (six steady-states) with influent COD concentrations ranging from (67,000 to 91,400 mg/l) and organic loading rates (OLR) between (0.5 and 9.5 kg COD/m3 /d). In this study, the system was considered to have achieved steady state when the operating and control parameters were within ± 10% of the average value. A 20-litre wa‐ ter displacement bottle was used to measure the daily gas volume. The produced biogas contained only CO2 and CH4, in order to collect pure CH4, the addition of sodium hydroxide solution (NaOH) will absorb CO2 effectively and the remaining will be methane gas (CH4).


**Table 2.** Summary of results (SS: steady state)

**Figure 2.** Schematic for Ultrasonicated membrane anaerobic system (UMAS)

110 International Perspectives on Water Quality Management and Pollutant Control

utilisation rate (SUR), and specific substrate utilisation rate (SSUR).

Raw POME samples were collected from a palm oil mill in Kuantan-Malaysia. The wastewa‐

mand (COD), total suspended solids (TSS), pH, volatile suspended solids (VSS), substrate

The ultrasonicated membrane anaerobic system, UMAS Performance was evaluated under six different inflow conditions (six steady-states) with influent COD concentrations ranging from (67,000 to 91,400 mg/l) and organic loading rates (OLR) between (0.5 and 9.5 kg

the operating and control parameters were within ± 10% of the average value. A 20-litre wa‐ ter displacement bottle was used to measure the daily gas volume. The produced biogas contained only CO2 and CH4, in order to collect pure CH4, the addition of sodium hydroxide solution (NaOH) will absorb CO2 effectively and the remaining will be methane gas (CH4).

/d). In this study, the system was considered to have achieved steady state when

C prior to use. Samples analysed for chemical oxygen de‐

**2.1. Palm oil mill effluent**

**2.2. Bioreactor operation**

COD/m3

ter was stored in a cold room at 4o


**Table 3.** Results of the application of three known substrate utilisation models

## **3. Results and discussion**

#### **3.1. Semi-continuous Ultrasonic-Membrane Anaerobic System (UMAS) performance**

Table 2 summarises UMAS performance of six inflow rates all (at six steady-states), which were established at different HRTs and influent COD concentrations. The kinetic coefficients of the selected models were derived from Eq. (2) in Table 1 by using a linear relationship; the coeffi‐ cients are summarised in Table 3. At steady-state conditions with influent COD concentrations of 67,000-91,400 mg/l, UMAS performed well and the pH in the reactor remained within the op‐ timal working range for anaerobic digesters (6.7-7.8). At the first steady-state, the MLSS concen‐ tration was about 12,960 mg/l whereas the MLVSS concentration was 10,091 mg/l, equivalent to 77.9% of the MLSS. This low result can be attributed to the high suspended solids contents in the POME. At the sixth steady-state, however, the volatile suspended solids (VSS) fraction in the re‐ actor increased to 88% of the MLSS. This indicates that the long SRT of UMAS facilitated the de‐ composition of the suspended solids and their subsequent conversion to methane (CH4); this conclusion supported by [31] and [32]. The highest influent COD was recorded at the sixth steady-state (91,400 mg/l) and corresponded to an OLR of 9.5 kg COD/m3 /d. At this OLR the, UMAS achieved 96.7% COD removal and an effluent COD of 3000 mg/l. This value is better than those reported in other studies on anaerobic POME digestion [33, 34]. The three kinetic models demonstrated a good relationship (R2 > 99%) for the membrane anaerobic system treating POME, as shown in Figs. 2-5. The Contois and Chen & Hashimoto models performed better, im‐ plying that digester performance should consider organic loading rates. These two models sug‐ gested that the predicted permeate COD concentration (S) is a function of influent COD concentration (So). In Monod model, however, S is independent of So. The excellent fit of these three models (R2 > 97.8%) in this study suggests that the UMAS process is capable of handling sustained organic loads between 0.5 and 9.5 kg m3 /d.

7 7.5 8 8.5 9 9.5 10 10.5

Ultrasonic Membrane Anaerobic System (UMAS) for Palm Oil Mill Effluent (POME) Treatment

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*X/S*

30 35 40 45 50 55 60 65 70

*1/U = 0.051\*(X) + 1.4 R2 = 0.987*

*So/S*

Fig.6 shows the percentages of COD removed by UMAS at various HRTs. COD removal ef‐ ficiency increased as HRT increased from 5.40 to 480.3 days and was in the range of 96.7 % - 98.5 %. This result was higher than the 85 % COD removal observed for POME treatment using anaerobic fluidised bed reactors [35] and the 91.7-94.2 % removal observed for POME treatment using MAS [36]. The COD removal efficiency did not differ significantly between HRTs of 480.3 days (98.5%) and 20.3 days (98.0%). On the other hand, the COD removal effi‐ ciency was reduced shorter HRTs; at HRT of 5.40 days, COD was reduced to 96.7 %. As shown in Table 2, this was largely a result of the washout phase of the reactor because the

*1/U = 0.47\*(X/S) + 0.12 R2= 0.978*

3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2

2.5

biomass concentration increased in the system.

**Figure 5.** The Chen and Hashimoto mdel.

3

3.5

*1/U (g VSS.d/g COD)*

4

4.5

5

**Figure 4.** The Contois model.

*1/U (g VSS.d/g COD)*

**Figure 3.** The monod model.

Ultrasonic Membrane Anaerobic System (UMAS) for Palm Oil Mill Effluent (POME) Treatment http://dx.doi.org/10.5772/54459 113

**Figure 4.** The Contois model.

**3. Results and discussion**

112 International Perspectives on Water Quality Management and Pollutant Control

three models (R2

sustained organic loads between 0.5 and 9.5 kg m3

3

**Figure 3.** The monod model.

3.5

4

4.5

**1/U (g VSS.d/g COD)**

5

5.5

**3.1. Semi-continuous Ultrasonic-Membrane Anaerobic System (UMAS) performance**

steady-state (91,400 mg/l) and corresponded to an OLR of 9.5 kg COD/m3

Table 2 summarises UMAS performance of six inflow rates all (at six steady-states), which were established at different HRTs and influent COD concentrations. The kinetic coefficients of the selected models were derived from Eq. (2) in Table 1 by using a linear relationship; the coeffi‐ cients are summarised in Table 3. At steady-state conditions with influent COD concentrations of 67,000-91,400 mg/l, UMAS performed well and the pH in the reactor remained within the op‐ timal working range for anaerobic digesters (6.7-7.8). At the first steady-state, the MLSS concen‐ tration was about 12,960 mg/l whereas the MLVSS concentration was 10,091 mg/l, equivalent to 77.9% of the MLSS. This low result can be attributed to the high suspended solids contents in the POME. At the sixth steady-state, however, the volatile suspended solids (VSS) fraction in the re‐ actor increased to 88% of the MLSS. This indicates that the long SRT of UMAS facilitated the de‐ composition of the suspended solids and their subsequent conversion to methane (CH4); this conclusion supported by [31] and [32]. The highest influent COD was recorded at the sixth

UMAS achieved 96.7% COD removal and an effluent COD of 3000 mg/l. This value is better than those reported in other studies on anaerobic POME digestion [33, 34]. The three kinetic models demonstrated a good relationship (R2 > 99%) for the membrane anaerobic system treating POME, as shown in Figs. 2-5. The Contois and Chen & Hashimoto models performed better, im‐ plying that digester performance should consider organic loading rates. These two models sug‐ gested that the predicted permeate COD concentration (S) is a function of influent COD concentration (So). In Monod model, however, S is independent of So. The excellent fit of these

> 97.8%) in this study suggests that the UMAS process is capable of handling

/d.

2 4 6 8 10 12 14

*1/U = 1.7e+003\*(I/S) + 2.8*

*R2 = 0.989*

**1/S (m3/kg COD)**

x 10-4

/d. At this OLR the,

**Figure 5.** The Chen and Hashimoto mdel.

Fig.6 shows the percentages of COD removed by UMAS at various HRTs. COD removal ef‐ ficiency increased as HRT increased from 5.40 to 480.3 days and was in the range of 96.7 % - 98.5 %. This result was higher than the 85 % COD removal observed for POME treatment using anaerobic fluidised bed reactors [35] and the 91.7-94.2 % removal observed for POME treatment using MAS [36]. The COD removal efficiency did not differ significantly between HRTs of 480.3 days (98.5%) and 20.3 days (98.0%). On the other hand, the COD removal effi‐ ciency was reduced shorter HRTs; at HRT of 5.40 days, COD was reduced to 96.7 %. As shown in Table 2, this was largely a result of the washout phase of the reactor because the biomass concentration increased in the system.

0 50 100 150 200 250 300 350 400 450 500

Ultrasonic Membrane Anaerobic System (UMAS) for Palm Oil Mill Effluent (POME) Treatment

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*Hydraulic retention time (days)*

**Figure 7.** Specific substrate utilization rate for COD under steady-state conditions with various hydraulic retention times.

**y = 0.41\*x + 0.26 R2= 0.972**

<sup>0</sup> 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.25

**1/HRT (day-1)**

0.18

0.26 0.27 0.28 0.29 0.3 0.31 0.32 0.33 0.34

**Figure 8.** Determination of the growth yield, Y and the specific biomass decay rate, b

**SSUR (kg COD/kg VSS/d)**

0.2

0.22

0.24

*Specific substrate utilization rate*

 *(kg COD/kg VSS/d)*

0.26

0.28

0.3

**Figure 6.** COD removal efficiency of UMAS under steady-state conditions with various hydraulic retention times.

#### **3.2. Determination of bio-kinetic coefficients**

Experimental data for the six steady-state conditions in Table 2 were analysed; kinetic coeffi‐ cients were evaluated and are summarised in Table 3. Substrate utilisation rates (SUR); and specific substrate utilisation rates (SSUR) were plotted against OLRs and HRTs. Fig. 7 shows the SSUR values for COD at steady-state conditions HRTs between 5.40 and 480.3 days. SSURs for COD generally increased proportionally HRT declined, which indicated that the bacterial population in the UMAS multiplied [37]. The bio-kinetic coefficients of growth yield (Y) and specific micro-organic decay rate, (b); and the K values were calculated from the slope and intercept as shown in Figs. 8 and 9. Maximum specific biomass growth rates (µmax) were in the range between 0.248 and 0.474 d-1. All of the kinetic coefficients that were calculated from the three models are summarised in Table 3. The small values of µmax are suggestive of relatively high amounts of biomass in the UMAS [38]. According to [39], the values of parameters µmax and K are highly dependent on both the organism and the sub‐ strate employed. If a given species of organism is grown on several substrates under fixed environmental conditions, the observed values of µmax and K will depend on the substrates.

**Figure 7.** Specific substrate utilization rate for COD under steady-state conditions with various hydraulic retention times.

0 50 100 150 200 250 300 350 400 450 500

*Hydraulic retention time (days)*

**Figure 6.** COD removal efficiency of UMAS under steady-state conditions with various hydraulic retention times.

Experimental data for the six steady-state conditions in Table 2 were analysed; kinetic coeffi‐ cients were evaluated and are summarised in Table 3. Substrate utilisation rates (SUR); and specific substrate utilisation rates (SSUR) were plotted against OLRs and HRTs. Fig. 7 shows the SSUR values for COD at steady-state conditions HRTs between 5.40 and 480.3 days. SSURs for COD generally increased proportionally HRT declined, which indicated that the bacterial population in the UMAS multiplied [37]. The bio-kinetic coefficients of growth yield (Y) and specific micro-organic decay rate, (b); and the K values were calculated from the slope and intercept as shown in Figs. 8 and 9. Maximum specific biomass growth rates (µmax) were in the range between 0.248 and 0.474 d-1. All of the kinetic coefficients that were calculated from the three models are summarised in Table 3. The small values of µmax are suggestive of relatively high amounts of biomass in the UMAS [38]. According to [39], the values of parameters µmax and K are highly dependent on both the organism and the sub‐ strate employed. If a given species of organism is grown on several substrates under fixed environmental conditions, the observed values of µmax and K will depend on the substrates.

96.6 96.8 97 97.2 97.4 97.6 97.8 98 98.2 98.4 98.6

**3.2. Determination of bio-kinetic coefficients**

*COD Removal efficiency (%)*

114 International Perspectives on Water Quality Management and Pollutant Control

**Figure 8.** Determination of the growth yield, Y and the specific biomass decay rate, b

**0 1 2 3 4 5 6 7 8 9 10**

**Gas yield CH4 yield**

Ultrasonic Membrane Anaerobic System (UMAS) for Palm Oil Mill Effluent (POME) Treatment

**0**

**0.5**

*Yield (l/g COD/d)*

**1**

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117

*Organic loading rate (kg COD/m3/d)*

The ultrasonic membrane anaerobic system, UMAS seemed to be adequate for the bio‐ logical treatment of undiluted POME, since reactor volumes are needed which are con‐ siderably smaller than the volumes required by the conventional digester. UMAS were found to be an improvement and a successful biological treatment system that achieved high COD removal efficiency in a short period of time (no membrane fouling by intro‐ duction of ultrasonic). The overall substrate removal efficiency was very high-about 98.5%. The gas production, as well as the methane concentration in the gas was satisfac‐ tory and, therefore, could be considered (the produced methane gas) as an additional en‐ ergy source for the use in the palm oil mill. Preliminary data on anaerobic digestion at

C in UMAS showed that the proposed technology has good potential to substantially reduce the pollution load of POME wastewater. UMAS was efficient in retaining the bio‐ mass.The UMAS process will recover a significant quantity of energy (methane 79%) that

could be used to heat or produce hot water at the POME plant.

**60**

**Figure 10.** Gas production and methane content

**5. Conclusions**

30 o

**70**

*CH4*

*% Methane*

**80**

**Figure 9.** Determination of the maximum specific substrate utilization and the saturation constant, K

## **4. Gas production and composition**

Many factors must be adequately controlled to ensure the performance of anaerobic digest‐ ers and prevent failure. For POME treatment, these factors include pH, mixing, operating temperature, nutrient availability and organic loading rates into the digester. In this study, the microbial community in the anaerobic digester was sensitive to pH changes. Therefore, the pH was maintained in an optimum range (6.8-7) (by addition of NaOH) to minimize the effects on methanogens that might biogas production. Because methanogenesis is also strongly affected by pH, methanogenic activity will decrease when the pH in the digester deviates from the optimum value. Mixing provides good contact between microbes and sub‐ strates, reduces the resistance to mass transfer, minimizes the build-up of inhibitory inter‐ mediates and stabilizes environmental conditions. This study adopted the mechanical mixing and biogas recirculation. Fig. 10 shows the gas production rate and the methane con‐ tent of the biogas. The methane content generally declined with increasing OLRs. Methane gas contents ranged from 68.5% to 79% and the methane yield ranged from 0.29 to 0.59 CH4/g COD/d. Biogas production increased with increasing OLRs from 0.29 l/g COD/d at 0.5 kg COD/m3 /d to 0.88 l/g COD/d at 9.5 kg COD/m3 /d. The decline in methane gas content may be attributed to the higher OLR, which favours the growth of acid forming bacteria over methanogenic bacteria. In this scenario, the higher rate of carbon dioxide; (CO2) forma‐ tion reduces the methane content of the biogas.

**Figure 10.** Gas production and methane content

### **5. Conclusions**

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

**y = 9.5e+002\*x + 2.7 R2 = 0.939**

**1/S (1/mg)**

Many factors must be adequately controlled to ensure the performance of anaerobic digest‐ ers and prevent failure. For POME treatment, these factors include pH, mixing, operating temperature, nutrient availability and organic loading rates into the digester. In this study, the microbial community in the anaerobic digester was sensitive to pH changes. Therefore, the pH was maintained in an optimum range (6.8-7) (by addition of NaOH) to minimize the effects on methanogens that might biogas production. Because methanogenesis is also strongly affected by pH, methanogenic activity will decrease when the pH in the digester deviates from the optimum value. Mixing provides good contact between microbes and sub‐ strates, reduces the resistance to mass transfer, minimizes the build-up of inhibitory inter‐ mediates and stabilizes environmental conditions. This study adopted the mechanical mixing and biogas recirculation. Fig. 10 shows the gas production rate and the methane con‐ tent of the biogas. The methane content generally declined with increasing OLRs. Methane gas contents ranged from 68.5% to 79% and the methane yield ranged from 0.29 to 0.59 CH4/g COD/d. Biogas production increased with increasing OLRs from 0.29 l/g COD/d at 0.5

may be attributed to the higher OLR, which favours the growth of acid forming bacteria over methanogenic bacteria. In this scenario, the higher rate of carbon dioxide; (CO2) forma‐

**Figure 9.** Determination of the maximum specific substrate utilization and the saturation constant, K

/d to 0.88 l/g COD/d at 9.5 kg COD/m3

tion reduces the methane content of the biogas.

2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8

**4. Gas production and composition**

kg COD/m3

**1/SSUR (day)**

116 International Perspectives on Water Quality Management and Pollutant Control

x 10-3

/d. The decline in methane gas content

The ultrasonic membrane anaerobic system, UMAS seemed to be adequate for the bio‐ logical treatment of undiluted POME, since reactor volumes are needed which are con‐ siderably smaller than the volumes required by the conventional digester. UMAS were found to be an improvement and a successful biological treatment system that achieved high COD removal efficiency in a short period of time (no membrane fouling by intro‐ duction of ultrasonic). The overall substrate removal efficiency was very high-about 98.5%. The gas production, as well as the methane concentration in the gas was satisfac‐ tory and, therefore, could be considered (the produced methane gas) as an additional en‐ ergy source for the use in the palm oil mill. Preliminary data on anaerobic digestion at 30 o C in UMAS showed that the proposed technology has good potential to substantially reduce the pollution load of POME wastewater. UMAS was efficient in retaining the bio‐ mass.The UMAS process will recover a significant quantity of energy (methane 79%) that could be used to heat or produce hot water at the POME plant.

**Author details**

UMP, Malaysia

Malaysia

**References**

N.H. Abdurahman1\*, N.H. Azhari2

gy (1996a): 45, 125-135.

nology 97, 686-691.

Jersey (2003): pp. 51-57.

ence.

53-62.

\*Address all correspondence to: nour2000\_99@yahoo.com

and Y.M. Rosli1

1 Faculty of Chemical and Natural Resources Engineering, University of Malaysia Pahang-

Ultrasonic Membrane Anaerobic System (UMAS) for Palm Oil Mill Effluent (POME) Treatment

http://dx.doi.org/10.5772/54459

119

2 Faculty of Industrial Sciences and Technology, University of Malaysia Pahang-UMP,

[1] Borja, R., C.J. Banks., E. Sanchez. Anaerobic treatment of palm oil mill effluent in a two-stage up-flow anaerobic sludge blanket (UASB) reactor. Journal of Biotechnolo‐

[2] Najafpour, G.D.., A.A.L, Zinatizadeh., A.R. Mohamed., M.Hasnain Isa., H.Nasrollah‐ zadeh. High-Rate anaerobic digestion of palm oil mill effluent in an upflow anaero‐

[3] Cote, C., I.M. Daniel., S.Quessy. (2006). Reduction of indicator and pathogenic micro‐ organisms by psychrophilic anaerobic digestion in swine slurries. Bioresource Tech‐

[4] Gee, P.T., N.S. Chua. (1994). Current status of palm oil mill effluent by watercourse discharge. In: PORIM National Palm Oil Milling and Refining Technology Confer‐

[5] Guerrero, L., F. Omil., R.Mendez., J.M. Lema. (1999). Anaerobic hydrolysis and acidogenesis of wastewater from food industries with high content of organic solids

[6] Gerardi, M.H.. The microbiology of Anaerobic Digesters. Wiley-Interscience, New

[7] linke, B. (2006). Kinetic study of thermophilic anaerobic digestion of solid wastes

[8] Chooi, C.F. Ponding system for palm oil mill effluent treatment. PORIM 9, (1984):

[9] Ma. A.N. Treatment of palm oil mill effluent. Oil Palm and Environment: Malaysian

bic sludge-fixed Film bioreactor. Biochemistry (2006): 41, 370-379.

and protein. Water Resource Journal 33, 3281-3290.

from potato processing. Biomass and Bioenergy 30, 892-896.

Perspective. Malaysia Oil Palm Growers' Council. (1999): p.277.

## **Appendix A. nomenclature**

COD: chemical oxygen demand (mg/l) OLR: organic loading rate (kg/m3 /d) CUF: cross flow ultra-filtration membrane SS: steady state SUR: substrate utilization rate (kg/m3 /d) TSS: total suspended solid (mg/l) MLSS: mixed liquid suspended solid (mg/l) HRT: hydraulic retention time (day) SRT: solids retention time (day) SSUR: Specific substrate utilization rate (kg COD/kg VSS/d) MAS: Membrane An aerobic System UMAS: Ultrasonicated Membrane Anaerobic System MLVSS: mixed liquid volatile suspended Solid (mg/l) VSS: volatile suspended solids (mg/l) MWCO: molecular weight Cut-Off BLR: biological loading rate U = specific substrate utilisation rate (SSUR) (g COD/G VSS/d) S = effluent substrate concentration (mg/l) So = influent substrate concentration (mg/l) X = micro-organism concentration (mg/l) : Maximum specific growth rate (day-1) K: Maximum substrate utilisation rate (COD/g/VSS.day) : Half velocity coefficient (mg COD/l) X: Micro-organism concentration (mg/l) b = specific microorganism decay rate (day-1) Y = growth yield coefficient (gm VSS/gm COD) T: time

## **Author details**

**Appendix A. nomenclature**

OLR: organic loading rate (kg/m3

SS: steady state

COD: chemical oxygen demand (mg/l)

CUF: cross flow ultra-filtration membrane

MLSS: mixed liquid suspended solid (mg/l)

SSUR: Specific substrate utilization rate (kg COD/kg VSS/d)

U = specific substrate utilisation rate (SSUR) (g COD/G VSS/d)

K: Maximum substrate utilisation rate (COD/g/VSS.day)

UMAS: Ultrasonicated Membrane Anaerobic System

MLVSS: mixed liquid volatile suspended Solid (mg/l)

SUR: substrate utilization rate (kg/m3

TSS: total suspended solid (mg/l)

HRT: hydraulic retention time (day)

MAS: Membrane An aerobic System

VSS: volatile suspended solids (mg/l)

S = effluent substrate concentration (mg/l)

So = influent substrate concentration (mg/l)

X = micro-organism concentration (mg/l)

: Maximum specific growth rate (day-1)

: Half velocity coefficient (mg COD/l)

T: time

X: Micro-organism concentration (mg/l)

b = specific microorganism decay rate (day-1)

Y = growth yield coefficient (gm VSS/gm COD)

MWCO: molecular weight Cut-Off

BLR: biological loading rate

SRT: solids retention time (day)

/d)

118 International Perspectives on Water Quality Management and Pollutant Control

/d)

N.H. Abdurahman1\*, N.H. Azhari2 and Y.M. Rosli1

\*Address all correspondence to: nour2000\_99@yahoo.com

1 Faculty of Chemical and Natural Resources Engineering, University of Malaysia Pahang-UMP, Malaysia

2 Faculty of Industrial Sciences and Technology, University of Malaysia Pahang-UMP, Malaysia

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120 International Perspectives on Water Quality Management and Pollutant Control


## *Edited by Nigel W.T. Quinn*

The level of surface water quality protection is variable around the world in large part due to the relative effectiveness of environmental regulation and the degree to which science influences the regulatory process. In the United States, at the federal level, the Total Maximum Daily Load (TMDL) has been an effective policy and water quality management tool for dealing with both point source and non-point source pollution. The TMDL provides a rational framework for estimating the assimilative capacity of the receiving water body for certain contaminants and applying factors of safety and incorporating acceptable levels of water quality criteria violation - provided the local stakeholders have a say in the decision making process. This collection of articles from around the world are good examples of the application of sound scientific principles to solve pressing water quality problems.

International Perspectives on Water Quality Management and Pollutant Control

International Perspectives on

Water Quality Management

and Pollutant Control

*Edited by Nigel W.T. Quinn*

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