Performance of HUASB reactor for
treating paper & Pulp wastewater using
Effective Microorganism(EM)
Er.N.Balasubramanian, M.E(Env.Engg), Research Scholar, Bharathi University, Dr.M.Muthukumar Ph.D,
Assistant Professor, Bharathiyar University,
Coimbatore
Abstract:
Pulp and paper industry is one of the most polluting industries all over the world that uses significant amount of fresh water and produces substantial amount of solid and liquid waste. Wastewater from this industry is potentially polluting nature and before discharge into natural course, it is mandatory to adhere to the discharge norms. Anaerobic treatment of paper processing wastewater has a distinct advantage of recovery of inherent energy in the form of methane gas with less sludge production. A hybrid reactor (HUASB) that capitalizes on the positive features of anaerobic filter (AF) and up-flow anaerobic sludge blanket (UASB). The main objective of the thesis is to find out the performance efficiency of the hybrid up-flow anaerobic sludge blanket (HUASB) reactor for treatment of pulp & paper mill wastewater using Effective Microorganism(EM). In this study, a lab-scale HUASB reactor of 9.68 litres and an effective volume of 7.88 L had been used at ambient temperature with PVC packing materials in the top one third of the reactor.
The reactor was initially filled with 2L of cow dung and 2L with seed sludge and remaining with pulp and paper mill wastewater. Start-up was successfully carried out for 130 days and a steady state condition has attained. The reactor was start with an initial influent COD of 750 mg/l, VFA of 65 mg/L with an Organic Loading rate (OLR) of 0.75 kg COD/m3.d and Hydraulic Retention Time( HRT) of 24 hours(hrs) and gradually OLR increased. In order to optimize HRT, various HRT were adapted from 24 hrs to 8 hrs and the maximum effluent COD removal of 83% was observed at a HRT of 12 hours with a gas production of 1.162 L/ L reactor volume/day and methane gas content observed as 71% with a rate of 0.28 m3/kg COD removed. After start up, treatment performance using Activated EM and higher OLR has been loaded for attaining steady state by increasing the influent COD concentration adopting HRT 12 hrs for a period of another 130 days. The maximum effluent COD removal efficiency of 92%, achieved with an OLR of 9.00 Kg COD/m3.day, with gas production of 3.2 L/L.day with 72% methane content and production rate of 0.29 m3/kg COD removed.
Introduction
Biological treatment process
Among the biological treatment methods, conventional aerobic methods are unattractive because of high energy cost for aeration and the cost of disposal of huge quantity of sludge generated as high as 50% of treatment cost. The anaerobic treatment system has the advantage of recovery of inherent energy in the form of biogas containing 75% of methane gas a high calorie fuel with less sludge formation. However, the conventional anaerobic system is not adequate enough to treat the paper and pulp wastewater to discharge into water bodies or on soil and hence anaerobic digestion is followed by aerobic treatment and tertiary treatment.
Lettinga and Van Haandel, 1994 studied the aerobic and anaerobic systems of waste treatment. They provided various results according to the parameter analyzed. The aerobic conversion of 1Kg of COD requires about 2 KWhr of energy and produces 0.5 kg of sludge and on the other hand in an anaerobic process 1 kg of COD gives rise to 0.35m3 of biogas and generates 0.1 kg of biomass as stable sludge. The sludge produced in the aerobic system is unstable and produces 0.2-0.3 kg VSS/Kg COD but in anaerobic treatment 0.05- 0.15kg VSS/ Kg COD sludge is produced and it is stable with high nutrient values. The growing interest in alternate sources of energy also intensified the development of anaerobic systems with low energy consumption than aerobic system.
Hybrid upflow anaerobic sludge blanket reactors (HUASBR)
The difficulties associated with UASB reactor such as clogging of the bed due to bio film thickness have given rise to the development of the hybrid reactor. The HUASB reactor was developed by Guiot and Van den Berg (1984). The HUASB reactor is a combination of up-flow anaerobic sludge blanket reactor and anaerobic filter. The lower part of the HUASB reactor consists of UASB portion where flocculent and granular sludge are developed. The upper part of the reactor serves as a fixed film reactor. The HUASBR has been successfully tested for the various industrial waste water generating in swine, soft drink, slaughter house, pulp & paper, coffee processing wastewater palm oil effluent, synthesis based pharmaceutical wastewater.(Pakhrel and Viraraghavan )2004
The HUASBR has several advantages such as
• Long solid retention time, since the filter media traps and retains the biological solids. • Minimized channeling and loss of biomass associated with UASB reactors.
• Packed zone acts as a GLS separator.
• Packing provides a zone of polishing biomass which improves process stability under transient
conditions.
Parameters affecting anaerobic digestion of HUASB Reactor
Hydraulic retention time is considered as very essential parameter to maintain an adequate up-flow velocity to assure good mixing to allow metabolism. In the treatment of cornstarch wastewater in UASB, rising of hydraulic retention time from 6h to 12h increases the removal efficiency of the COD and methane production rate.(Lettinga et al)
Effective Microorganisms (EM) is a group of organisms that has a reviving action on humans, animals, and the natural environment and has also been described as a multi – culture of coexisting anaerobic and aerobic beneficial microorganisms (Higa 1995) & (EM Trading 2000). The basis for using these EM species of microorganisms is that they contain various organic acids due to the presence of lactic acid bacteria, which secrete organic acids, enzymes, antioxidants, and metallic chelates. One of the major benefits of the use of EM is the reduction in sludge volume. Theoretically, the beneficial organisms present in EM should decompose the organic matter by converting it to carbon dioxide (CO2), methane (CH4) or use it for growth and reproduction.
Methodology
Reactor set-up & Performance study
The gas outlet was connected through rubber tubing to the liquid displacement system to measure the gas production. The amount of gas produced is directly proportional to the amount of liquid displaced and hence gas produced can be measured at regular intervals of time. A PVC filter media was provided at the middle of the reactor. The reactors were operated at mesophilic temperature (27±5°C). The wastewater comprising substrates, balanced nutrients were fed in the reactor using a peristaltic pump. The initial characteristics of the pulp & Paper mill wastewater (wash water of bagasse) is shown in Table 1.
Table.1 Initial concentration of pulp and paper mill wastewater
*Range of 5 samples Start-up of the reactor
For an anaerobic treatment plant, the startup is a time consuming process due to fact that the bacterial population to be developed as to the particular characteristics of the wastewater for which inoculums are required. Rate of start-up depends on the type of inoculums, the type and strength of waste, level of volatile acids maintained. Anaerobic seed culture collected from the reactor of a biogas plant was used for the inoculation in HUASB reactor. The seed sludge comprised of 10,560 mg/L of VSS with a low SLR of 0.08 Kg COD/ Kg of VSS.day. The reactor was operated in a continuous mode of operation. The feed composition of the HUASB reactor was maintained in the ratio COD: N: P around 200:5:1.
The reactor was initially filled with 2Litrer of cow dung and 2Litre of seed sludge and obtained from a biogas plant and the remaining with pulp and paper mill wastewater gradually. Initial feeding rate was 7.8 L/day which corresponds to 24 hours HRT. The reactor was started with an initial COD of 750 mg/L with an organic loading rate of 0.75 kg COD/ m3.d. OLR was increased in steps by decreasing HRT and varying flow rates over a period of 130 days. The summary of all parameters shown in figures 2 and 3.
Treatment Phase of the Reactor
After the start up with granulation activated Effective Micro-organisms (EM) solution was added in 1:1000 ratio of reactor volume daily. OLR was increased gradually by increasing COD of pulp and paper mill wastewater concentration at constant HRT of 12 hours. The reactor was closely monitored for parameters like pH, Volatile Fatty Acid (VFA), COD, Biogas production and its Methane content, Alkalinity during entire operation periods.
SL.NO. PARAMETERS Ranges mg/l *
1. pH 5.2-6.5
2. Total solids 4000-4500
3 Total suspended solids 1000-1200
4 Volatile solids 1000-1500
5 Alkalinity 400-800
6 Acidity 1000-1200
7 Chlorides 700-900
8 COD 2000-6000
9 BOD 900 - 2500
10 Electrical Conductivity
(ms/cm) 2.20-2.22
Chemical Analysis
COD, VFA as acetate, total alkalinity were analysed adopting standard methods (1998). Methane content was analysed by Gas Chromatography.
Results
The loading and biogas production of the reactor during the startup are presented in figure 2 and 3. The OLR applied during start up period was 0.75 kg COD/m3.d at a HRT of 24 hours. OLR was increased in a stepped manner to 4 kg COD/m3.d over a period of 130 days. In order to optimize HRT, various HRT rates were adapted from 24 hrs to 8 hrs. The biogas production increased and reached a maximum of 1.162 L/L of reactor volume/day at an OLR of3.60 kg COD/m3.d with 83% COD removal at a HRT of 12 hours. The Methane gas content of 72% with a rate of 0.28 m3/kg COD removal was observed.
Performance of reactor after start up
Fig.5 & 6 illustrates the loading pattern and biogas production during the treatment. The initial OLR applied during this phase was1.1 kg COD/m3.d. It was increased in a stepped manner to 13 kg COD/m3.d over a period of 260 days. The gas production increased as OLR increased, reaching a maximum of 3.2 m3/ kg COD removal at an OLR of 9 kg COD/m3.d. Beyond this loading, the gas production decreased. The ratio of VFA/Alkalinity show the variation of 0.1 to 0.13 upto an OLR of 9 kg COD/m3.d indicating healthy anaerobic environment and satisfactory methanogenic activity. After that the ratio of VFA/Alkalinity change from 0.2 to 0.61 (Raj Kumar et al, 2008) indicating souring of the reactor. The methane content in the biogas varied from 61% to 72%. The maximum effluent COD removal efficiency of 92% achieved, with an OLR of 9.00 Kg COD/m3.day, with gas production of 3.2 L/L.day with 72% methane content and production rate of 0.29 m3/kg COD removed (as to the studies supported by Karamany et al 2011, who’s efficiency attained 91%). The pH of the treated water was 6 at an OLR of 13 Kg COD/m3.day Alkalinity of the effluent increased from 882 mg/L at an OLR of 1.1 Kg COD/m3.day to 900 at an OLR of 13 Kg COD/m3.day from figure 4. Decreased in Alkalinity obviously affects the reactor performance.
Conclusion:
After 130 days, the HUASB reactor could able to start with successful granulation (Fig 7 & 8). Optimum HRT was found to be 10 hrs at optimum HRT the COD removal % of 92 with a gas yield of 3.2 L/L.day with a methane production rate of 0.29 m3/Kg COD removed. The performance of reactor was considerably increased when introducing EM into the reactor to a tune of 92%.
Performance of HUASB during start up
0 20 40 60 80 100 120 140
0 100 200 300 400 500 600 700 800 900
0 20 40 60 80 100 120 140
VFA in
mg/L
Alkalinity in
mg/L
Time Vs Alkalinity & VFA
Fig.2
Performance of HUASB after start up using EM
Fig.3
0 0.2 0.4 0.6 0.8 1 1.2 1.4
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50
0 20 40 60 80 100 120 140
Biogas
in
L/L
day
OLR in
Kg/m3.day
Time in days
Time Vs OLR & Bio gas production
OLR in Kg COD m3/day Biogas L/L. day
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
130 150 170 190 210 230 250
Eff. pH
OLR in
Kg
COD/m3.day
Time in days
Time Vs OLR & Eff. pH
OLR in Kg COD m3/day
Fig.4
Fig.5
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
600 800 1000 1200 1400 1600 1800
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Eff. pH
Alkalinity mg/L
OLR in Kg/m3.day
OLR Vs Alkalinity & Eff. pH
Alkalinity
Effluent pH
0 10 20 30 40 50 60 70 80 90 100
0 100 200 300 400 500 600
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
VFA
COD removed
in %
OLR in Kg/m3.day
OLR Vs COD removal & VFA
VFA
Fig.6
SMA Analysis at end of Startup
Fig.7
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50
50 55 60 65 70 75 80 85 90 95
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Biogas L/L
day
COD
removed
in %
OLR in Kg/m3.day
OLR Vs COD removal & Bio gas
production
COD % removal
Fig.8
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