BULKING AGENT VARIATION IN AERATED STATIC PILE METHOD FOR SLUDGE PRODUCED WATER UTILIZATION AS SOIL
AMELIORANT
Agus Jatnika Effendi1 & Mahesa Gilang A.P2
1 & 2)Environmental Engineering Study Programme – Faculty of Civil & Environmental Engineering -
Institut Teknologi Bandung Jl Ganesha 10 Bandung 40132
email:jatnika@indo.net.id1
Abstract: One of the main wastes produced from oil and gas activity is sludge from produced water treatment.
According to Indonesia Government Regulation No. 18/1999 junto PP 85/1999 regarding hazardous waste management, this sludge is classified as hazardous waste. However, the characteristics of the sludge indicated that it could be utilized as soil ameliorant. Since the organic content of this sludge was very high (over 77%) and the Total Nitrogen Kjedahl (NTK) was very poor (1%), making the C/N ratio was too high. To reduce the C/N ratio, composting process was applied. Aerobic composting with aerated static pile method was expected to degrade the organic content and at the same time, to increase nitrogen content by means of nitrogen fixation process. The addition of bulking agent would increase the soil porosity as well as its hydraulic conductivity. The mixture of sludge and bulking agent after being processed was proven to comply the minimal technical requirement soil ameliorant according to Indonesian Ministry of Agriculture no. 70/2011. After aerated for over 40 days, the C/N ratio was able to reach around 15-25 depending on the variation of type and composition of bulking agent. The used of dry leaves as bulking agent with composition ratio 1:3 ratio was found to be the most as the optimum composition.
Keywords: aerated static pile, bulking agent, produced water, sludge, soil ameliorant
INTRODUCTION
Produced water is wastewater that comes out of the drilling wells along with oil and gas, which is then separated from the oil/gas during the production process using a separator technology (Veil, 2004). One of the oil and gas industry by-product is sludge produced water, which is a residue from the produced water treatment when oil and solid is separated and continued by biological treatment in activated sludge unit (ASU). Sludge produced water is formed from the biological wastewater treatment process so that the characteristics of the content is still potentially have similarities despite being in different phases, namely semi-solids or solids. In the biological process oxygen and nutrients (nitrogen and phosphorus) are supplied in order to fasilitate microorganisms to grow The addition of a bulking agent in the mixing can indeed add to the pile of unused areas and costs, but the addition is in the right amounts can help the process of decomposition. In the composting process of bulking agent can help provide the energy source for microbes, assist the entry of sufficient air flow through the pores, keeping moisture, temperature, C / N ratio, and many other supporting aspects.
It had been a lot of bulking agent proven effective to help in the decomposition of sludge such as wheat, rye, corn straw, cotton waste, sawdust, wood chips, and grass (Peredes, 2010), so the clarifier sludge collected on activated sludge system will have a high BOD (biological oxygen demand), high COD (chemical oxygen demand), many resins, and also fatty acids. (Chong, 1993). Based on Government Regulation no. 18/1999, sludge produced from industial
There are three alternative technologies can be applied for sludge produced water handling; they are disposal by landfill technique, active treatment & processing through waste physical- chemical destruction process such as incineration process by combustion technology and utilization of the sludge via biological processes that can be resulted to the intended composition and structure. Since sludge produced water is categorized as hazardous waste, treating the waste is a must. However, the characteristics of sludge produced water indicates that sludge utilization is really possible thing to do for many purpose (Ize-Iyamu, 2011; Dong, 2008). In a decomposition process, very high C/N ratio will cause excess carbon and also cause the composting process to slow down. This occurs in the absence of sufficient amounts of nitrogen for microbial growth so that composting will remain in the low temperature that slowing the degradation process. According to Epstein (1997), higher C/N ratio in the composting process causes the slowdown due to supply nitrogen thin that inhibit cell growth. When these cells die, new elements contained N will again be used. Meanwhile, when the C/N ratio is too low, it will cause the loss of N from pile through evaporation as ammonia smell. C/N ratio is ideal for biological process to occur is 25-30 (Epstein, 1997).
The addition of a bulking agent can help the process of decomposition. In the decomposition process, bulking agent can help provide the energy source for microbes, assist the entry of sufficient air flow through the pores, keeping moisture, temperature, C/N ratio, and many other supporting aspects. In his research Berhte et al (2007) stated that good porosity for air supply would be around 30-36%. Soil porosity around 60-65% figure is a good value. However, the excess of bulking agent can result in very high porosity thus increasing the potential for temperature loss. Loss of temperature can lead to the absence of thermophilic bacteria. Soil porosity above 75% is classified as too excessive porosity. It had been a lot of bulking agent proven effective to help in the decomposition of sludge such as wheat, rye, corn straw, cotton waste, sawdust, wood chips, and grass (Peredes, 2010).
METHODOLOGY
Sludge produced water in this study, called bio-sludge, was taken from wastewater treatment plant (WWTP) of oil & gas industry in Indonesia, spesifically from activated sludge unit (ASU).
Bio-sludge was mixed with bulking agents with several varieties as shown in table 1 in order to increase the soil porosity. LOI (lost on Ignition), pH, C-Organic, NTK, water content, and TPH of the bio-sludge were characterized
Table 1 Bulking Agent & Bio-sludge Composition
No
Reactor Bulking agent Bulking agent:bio-sludge composition 1 Mixture of dry
leaves
1:1
2 1:2
3 1:3
4
Sawdust
1:1
5 1:2
6 1:3
7 Control Bio-sludge
Aerated static pile reactor as shown in figure 1, was simulated in a plastic container (30x25x20 cm). Since aerobic composting was expected to occur, the reactor is equipped with aeration system by using blower and perforated pipe to enhance the air streams coverage. Reactors were equipped with inspection pipe for the O2 and CO2 monitoring.
Figure 1. Reactor design.
C-Organic and NTK as the main parameters in this research were determined every 5 days. The other parameters such pH, temperature, and moisture content were also checked to keep the reactors under optimal condition. The process was observed until the value of C/N ratio meet the minimum technical requirement for industrial waste utilization as a soil ameliorant as required by Ministry of Agriculture Decree No. 70/2011.
RESULTS AND DISCUSSION
Bio-sludge contained a very high concentration of C-organic. It appears that bio-sludge could be categorized as combustible matters as indicated by the high carbon Loss On Ignition (LOI), reaching 89-92%. The overall result of the initial characterization was shown in Table 2. Since the ratio between C-Organic and NTK was too high, it is required to treat the bio-sludge in order to be utilized as soil ameliorant. Based on the characterization results below, it appeared that the C-organic content in bio-sludge indicated the potential to be processed by the biological treatment approach considering the bio-sludge has a high enough carbon source.
Table 2. Initial characteristic results of Bio-sludge Parameters
Bio-sludge
Value Unit Composting Ideal Criteria
C-Organic 77.73 %DW -
NTK 0.77 %DW -
C/N 103.85 - 25-30
pH 6.31 - 6.5-8.5
TPH 39 ppm Max 150000*
Moisture 97 % 50-60
Water Content 46.75 % -
*Indonesian Environment Ministry Decree No.128 Tahun 2003
The purpose of bulking agent addition was to make the physical structure of the bio-sludge suitable for biological process to occur, especially to keep the reactor under aerobic condition and at the same time, NTK value would be increased as a result of the nitrogen fixation process by the microorganisms. The initial characteristics of the bio-sludge and bulking agent mixtures are shown in Table 3.
Table 3. Bio-sludge & bulking Agent Mixtures Characteristics
From figure 2, it could be seen that the higher the ratio between bio-sludge and bulking agent the faster the decline of C Organic occurred in the reactors. It was indicated in reactors 1, 2, 4, and 5 that were used bulking agent in a ratio of 1: 1 and 1: 2 compared to the use of a bulking agent in a ratio of 1: 3. At a ratio of 1: 3, the volume of bio-sludge was three times as much as a bulking agent so that the porosity characteristics of the mixture were less permeable structure. Therefore, this resulted in air and oxygen transferring more difficult.
Figure 2. C-Organic Degradation
Generally, in the reactors with dry leaves as bulking agent, higher degradation rate was obtained compare to sawdust. The particle size of the sawdust is the smaller than dry leaves making the pores size created by sawdust smaller than those using dry leaves as bulking agent. Therefore, in
20.00$
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60.00$
70.00$
80.00$
90.00$
100.00$
0$ 5$ 10$ 15$ 20$ 25$ 30$ 35$ 40$ 45$
C"Organic*
Day*
Reactor$1$
Reactor$2$
Reactor$3$
Reactor$4$
Reactor$5$
Reactor$6$
Control$
Parameters
Results
Unit Composting Ideal Criteria Reactor
1 Reactor
2 Reactor
3 Reactor
4 Reactor
5 Reactor
6 control
C 75.28 54.42 78.19 73.93 86.77 73.73 77.00 %DW -
N 0.35 0.54 0.54 0.58 0.53 0.48 0.77 %DW -
C/N 214.96 101.52 145.87 126.66 163.53 154.75 108.45 - 25-30
pH 7 7.3 7.2 7.05 7 7.1 6.31 - 6.5-8.5
Moisture 60 81.6 75 60 73.25 87.5 97 % 50-60
the reactor which using dry leaves, the air to be easier reach all of the area so the oxygen will be well supplied and distributed. The degradation rate of C-organic is shown in table 4. Compared to the control reactor, C-Organic degradation rate in others reactor were having higher rate. This occurred due to no bulking agent was added to the control reactor, so oxygen supplied was very limited.
Table 4. C-Organic Degradation Rates
Reactor Degradation Rate (% C-Organic/day)
1 1.31
2 0.95
3 0.96
4 0.92
5 1.24
6 0.71
Control 0.56
Looking at the off gas measurement, in this case were O2 and CO2, proving that O2 as electron acceptor in aerobic biological process was consumed, while CO2 was released to the atmosphere as metabolism product. Within 10 days measurement, the O2 concentration was lower than normal atmospheric concentration (around 20%). It was in the range of 13.2-13.4 %. In contrast with the CO2 measurement, the concentration in day 0 measurement was around 0.02%, whereas the next 10 days measurement the value increased to the range of 0.06-0.09%. The increase of O2
and followed at the same time by the decrease of CO2, indicated that aerobic decomposition of C-organics was occurred.
The trend of NTK value in all reactors was increasing as shown in Figure 4. At the beginning of the process, it was in the range of 0-1%, and then after 40 days of operation, NTK concentration in all the reactors has reached 2%. The increase of NTK concentration due to static aerated pile system. Air consists of around 78% nitrogen in N2 form. In nitrogen cycle, the N2 nitrogen in the atmosphere is fixated by the bacteria into ammonium form ((NH4+). The presence of ammonium would be measured as NTK (Mihelcic, 1999). Compared the control which was not equipped by aeration system, it could be seen that the Nitrogen fixation is much slower than the aerated static pile.
Figure 4. The Occurring of Nitrogen Fixation
As shown in figure 5, it can be seen that the increase of NTK concentration and the decomposition of C-Organics followed by the reduction of C/N ratio. All reactors were proven to be able to reduce the C/N value significantly compared to the control reactor. However, the C/N ratio of reactor 2 and 5 were too low and below the requirement for soil ameliorant as stated in Ministry of Agriculture Decree No.70/2011.
Figure 5. The Decrease of C/N Ratio
Since the variation of bulking agents type and volume demonstrated no big difference performances of aerated static pile reactors, the 1:3 ration by using dry leaves as bulking agent was considered to be more applicative. The product of composting from this aerated static pile reactor was then characterized to compare with another requirements stated in Ministry of Agriculture Decree No.70/2011. The result of the characterization can be seen in Table 5.
Table 5. Final Characterization Results
0.00#
0.50#
1.00#
1.50#
2.00#
2.50#
3.00#
3.50#
0# 5# 10# 15# 20# 25# 30# 35# 40# 45#
NTK$(%DW)$
Days$
Reactor#1#
Reactor#2#
Reactor#3#
Reactor#4#
Reactor#5#
Reactor#6#
Control#
0.00#
20.00#
40.00#
60.00#
80.00#
100.00#
120.00#
140.00#
160.00#
180.00#
200.00#
220.00#
240.00#
0# 5# 10# 15# 20# 25# 30# 35# 40# 45#
C/N$
Days$
Reactor#1#
Reactor#2#
Reactor#3#
Reactor#4#
Reactor#5#
Reactor#6#
CONTROL#
It demonstrated that from technical standard results, the composting product using aerated static pile could be used as soil ameliorant. Since the macronutrients were found to be a little bit deficiency, the product could not be used as organic fertilizers. It could be only used as soil ameliorant. Physical composting products were also tested as shown in Table 6. They were Gs (specific gravity), n (porosity), Sr (saturated degree), the volume of air, water, and soil, and particle size distribution.
Table 6. Physical Characteristics
No Parameter Value
1 Gs/Specific Gravity 1,69
2 n 0,78
3 Sr (%) 19
4 Air Volume – Vg (%) 63,82
5 Water Volume – Vw (%) 14,51
6 Soil Volume – Vs (%) 21,67
7 Particle Size Distribution (PSD)
No Parameter Unit Quality
Standard Value Remark
1 C-Organic % Min 15 48.15 As required
2 C/N 15-25 19.13 As required
3 Unwanted Materials (plastic, glass,
gravel) % Max 2 0 As required
4 Kadar Air % 15-25 20.85 As required
6 pH 4-9 6.87 As required
7 Macro Nutrient (N+P2O5+K2O) % Min 4 3.09 Too low
8
Pathogenic Bacteria E Coli
MPN/gr Max 100 19 As required
Salmonella Sp Max 100 0 As required
9
Micro Element Fe Total or
ppm
Max 9000 3201 As required
Fe available Max 500 Not
necessary
As required
Mn Max 5000 171 As required
Zn Max 5000 110 As required
Cu Max 5000 9 As required
Mo Max 20
10 Na total ppm Max 2000 0.12 As required
11 Cl total ppm Max 5000 0.05 As required
No Parameter Value
#200 Sand Size (%) 29
Silt Size (%) 9
Clay Size (%) 0
% finer by weight passing sieve #200 9
The composting products was found to have a large volume of gas equal to 63.8% compared to the volume of water which was only 14.51%. The volume of void (Vv), which is a combination of air and water volume of compost products, was 78%. In other words, the porosity of composting product was 0.78 making it as a very good soil ameliorant. Moreover, with porosity owned by this product, it could be used as a bulking agent for further composting process.
Therefore, there is no need to find bulking agent such as dry leaves for the continuation of composting bio-sludge. Based on particle size distribution, this composting product could be classified as sandy loam or loamy sand. According to Brady (1990) in the book Principles of Soil Chemistry by Tan (1998), this type of soil is good material for gardening because of its structure that gives good water drainage.
CONCLUSION
Sludge from biological process of produced water treatment or so-called bio-sludge was proven to be a potential source for soil ameliorant or even organic fertilizer. The composting process by means of aerated static pile to achieve aerobic decomposition was able to decrease the C- organics content and at the same time to increase NTK concentration. Ideal ratio of C/N could be achieved within 40 days. The addition of bulking agent such as dry leaves and sawdust demonstrated to increase the bio-sludge porosity. Therefore, the aerobic composting process occurred under suitable condition. Although the variation of bulking agents type and volume showed no significant effect to the C/N ratio, the use of dry leaves with 1:3 composition was found to be the most effective variation. The composting product was also found to meet the technical standard as soil ameliorant stated in Indonesian Agriculture Ministry Decree no.
70/2011. However, the effectiveness and environmental risks of the composting product from bio-sludge of produced water should be further determined.
References
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