INTRODUCTION:

Increasing discharge and improper management of domestic waste water have created a great concern among the environment. An understanding of the chemical composition of waste water is important since this allows an understanding of reactions and interactions with the organic and inorganic compounds (Roila et al).The untreated domestic waste water contains numerous pathogenic microorganisms that dwell in the human intestinal tract. There is a need for the protection of the public health in a manner commensurate with environmental, economic, political and social concerns (Metcalf and eddy).

The conventional technologies followed for the treatment of domestic wastewater are less efficient in removing pathogenic organisms despite substantial removal of dissolved organics (Sekaran et al., 2006). Hence application of biological methods such as fluidized bed reactors has generated a lot of interest in the recent past in the field of waste water treatment processes due to its high performance efficiency compared to the conventional suspended growth and fixed-film waste water treatment processes. The major advantage of fluidized bed reactor over other biodegradation systems is a higher biomass concentration, and a higher mass transfer, resulting in a higher rate of biodegradation. Therefore the main aim of the present study is to evaluate the effectiveness of reducing the organic pollutant in the waste water through Fluidized Immobilized Carbon Catalytic Oxidation cell reactor with minimum sludge production which is a pioneering technology. In this study rice husk carbon is used as the catalyst, in which the contaminants adsorb the catalyst. As the contaminated water stream passes through a confined bed of rice husk carbon, a dynamic condition develops which establishes a mass transfer zone. By using rice husk, the contaminants adsorb to the surface of carbon. The immobilized-cell treatment system allows for increasing efficiency through the reduction of excess sludge production. The focal theme of the present investigation is to demonstrate the performance of FICCO reactor system for the effective removal of dissolved organics expressed as Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) in the domestic sewage waste water collected from Central Leather Research Institute.

MATERIALS AND METHODS:

SEWAGE WASTE WATER COLLECTION:

The sewage waste water was collected from sewage treatment plant at Central Leather Research Institute. The collected samples were analyzed for physicochemical parameters such as pH and total dissolved solids, pH, BOD, COD, Sulphides, sulphates, oil and grease and surfactant as per standard protocol.

PREPARATION OF RICE HUSK CARBON:

Rice husk as the precursor material obtained from the agricultural industry was well washed with H₂O several times for the removal of dust and used after oven drying at 110 °C for 6 h. The dried samples were then sieved to about 600-ím in size, and this fraction was used for the preparation of carbon. Porous carbons were prepared in two sequential steps: precarbonization and chemical activation. In the precarbonization process, the rice husk was heated at 400°C at the rate of 10 °C/min for about 4 h under N atmosphere and cooled to room temperature at the same rate. The resulting material is labeled as precarbonized carbon (PCC). The precarbonized carbon is subjected to chemical activation. In the chemical activation process, 50 g of the precarbonized carbon was agitated with 250g of aqueous solution containing 85% H₃PO₄ by weight. The ratio of chemical activating agent to precarbonized carbon was fixed at 4.2. The chemical activant and precarbonized carbon were homogeneously mixed at 85°C for 4 h. After being mixed, the precarbonized carbon slurry was dried under vacuum at 110 °C for 24 h. The resulting samples were then activated in a vertical cylindrical furnace under N₂ atmosphere at a flow rate of 100 mL/min. This was followed by heating to one of three different temperatures, namely, 700, 800, and 900°C, at a heating rate of 5 °C/min using a programmer and maintained at the final temperature for 1 h before cooling. After being cooled, the activated carbon was washed successively several times with hot water until the pH became neutral and finally washed with cold water to remove the excess phosphorus compounds. The washed samples were dried at 110 °C to obtain the final product. The samples heated at activation temperatures of 700, 800, and 900 °C were labeled C700, C800, and C900, respectively.

DESIGN AND SELECTION OF FICCO REACTOR:

An acrylic sheet reactor of height 12 cm and width 9 cm was fabricated. 6 such reactors were fabricated [Fig 1] with different dimensions of upper hopper and differing in the provision for aeration. The volume of the reactor was 740mL with working volume of 620mL the reactor was then filled with 12g of rice husk carbon and provision was made to distribute air in the fluidized bed to facilitate oxygen transfer for oxidation. The sewage waste water was fed into the reactor from the bottom. Among these the most efficient upflow reactor was selected on the basis of COD removal efficiency]. The most efficient reactor was selected for further study. The COD and BOD removal efficiency was estimated by adding different concentrations of surfactant, starch, oil and grease and protein. The parameters optimized include time and catalyst loading. In addition to these the raw water and FICCO treated water were analyzed for characteristics which include pH, sulphates, chloride, COD, BOD, total solids, dissolved solids and suspended solids level [Table 2].

Fig 1: Fabricated reactors with different dimensions of upper hopper.

EFFECT OF TIME:

To determine the maximum time required for the oxidation process in FICCO reactor, the experiment was conducted at specific time intervals. The samples were taken at 10, 20, 30, 45, 60, 120, 180, 250, 300 mins and the COD and BOD removal efficiencies was studied with and without using catalyst with respect to time.

EFFECT OF CATALYST LOADING:

To see the effect of catalyst on oxidation process, an experiment was conducted with and without catalyst. The catalyst used for oxidation process in the FICCO reactor is rice husk carbon. The catalyst was loaded in the reactor on varying concentrations from 1g to 15g. The COD and BOD removal efficiencies were observed for each varying concentrations of catalyst loading.

EFFECT OF DIFFERENT NUTRIENT LOADING ON THE COD REMOVAL:

A known volume of surfactant (20ml) was added to 1 litre of waste water such that the initial COD was maintained at the range of 800mg/l. After 2 hrs the inlet and outlet samples were taken to estimate the COD and BOD removal efficiency. Experiments were also done to estimate the amount of non-ionic surfactant present in the inlet and outlet samples. On running the reactor for six days a notable amount of sludge was collected and characterized for its quality.

Significant amount of proteins in the domestic waste water requires the use of biological process to reduce the COD levels. In order to find the COD and BOD removal efficiency by degradation of proteins, 2ml of fermented flesh was added to 1 litre of waste water for which the COD value reads approximately 800mg/l. After treating the waste water with FICCO reactor, the initial and FICCO treated water were estimated for COD and BOD removal efficiency. The protein content was also estimated for the inlet and outlet samples by lowry’s assay. The quality of sludge produced after 6 days of oxidation was also studied.

The efficiency of the reactor in degrading lipid content of the domestic waste water was also studied. 1% solution (1ml of fried oil in 100ml distilled water) of fried oil was taken and it was sonicated for 5 min. From the sonicated fried oil 20ml was added to 1 liter of waste water by maintaining the COD value around 800mg/l. The lipid content present in the inlet and outlet samples was also estimated. In addition the sludge produced by the rector after 6 days was also analyzed.

The influence of starch on COD and BOD removal efficiency for the inlet and outlet samples were studied by adding 20ml of starch from the prepared 5% solution of starch to 1 liter of waste water. The COD value of inlet sample after adding starch was in the range of 800mg/l. The amount of starch present in the inlet and outlet samples were also estimated. Sludge characterization of the sludge generated after 6 days of oxidation was done.

RESULTS AND DISCUSSION:

Characteristic of sewage:

The characteristics of sewage was analyzed freshly soon after the collection. The quality of the sewage in initial condition and after treating from FICCO reactor is presented in the Table 1.

Reactor performance:

The startup of the immobilized- cell reactor system was operated in a continuously sufficient aeration condition. An inlet flow containing a fixed concentration of COD and BOD was continuously fed into the reactor at a hydraulic retention time (HRT) of 3 hrs. The COD and BOD removal efficiencies of all the six reactors are mentioned in the Table 3. It was observed that the reactor C shows the maximum efficiency consistently. The dimensions of the reactor C was 12 x 9 x 9 cm with the length of liquid solid separator as 3.5cm. Since the surface area of the solid liquid separator is more the sludge particles settles down. There is no chance of moving up in to the upper hopper and therefore increases the efficiency of the reactor.

Table 1: Physicochemical parameters for raw domestic waste water and FICCO treated waste water.

S.No	Parameters	Raw waste water	FICCO Treated
1.	pH	7.6 ± 0.6	8.2 ± 0.2
2.	BOD	171.1 ± 51.7	79.3 ± 5.2
3.	COD	514.7 ± 154.6	238.1 ± 16.5
4.	Total suspended solids	187.1 ± 60	82.6 ± 9.6
5.	Nitrogen	50.2 ± 21.6	31.1 ± 5.8
6.	Sulphate	36.1 ± 10.3	16.3 ± 5.9
7.	Chlorides	40 ± 6	13.2 ± 3.7
8.	Surfactant	11.1 ± 3.1	4.47 ± 0.4
9.	Oil and Grease	60 ± 8.9	16 ± 1.8

Effect of time:

Fig. 3 shows the percentage removal of COD and BOD with and without adding catalyst varying with time. The percentage removal of COD without using catalyst increased linearly up to 3 h and was followed by a non-linear increase up to 57% in 5 h. The initial linear increase in COD reduction may be attributed to the chemical oxidation of the dissolved organics in the wastewater. In catalytic oxidation of organics using catalyst, the percentage removal of COD with time also followed an initial linear increase and then followed by a nonlinear increase. The percentage reduction in COD increased slowly to 91.6% in the catalytic oxidation using rice husk carbon as catalyst of the domestic wastewater in about 5 h. The catalytic oxidation removed BOD by 46% and 84% with and without carbon respectively.

Effect of catalyst loading:

On performing the oxidation process without any catalyst, it was observed that there was not much reduction in the COD and BOD. The COD and BOD reduction efficiency through this experiment was only 25% and 28% respectively. Thus the significance of catalyst loading was elucidated with the experiment without catalyst. Fig. 2 shows the effect of catalyst mass loading on COD during the catalytic oxidation of domestic waste water. The percent reductions of COD increased with the increase in catalyst loading from 1 to 12 g/620ml. With further increase in catalyst mass loading from 12 to 15 g/620ml, there has been no increase in percent COD removal. The catalyst concentration of 12 g/620ml may thus be considered as the optimum concentration at the given operating conditions. The maximum COD removal obtained at 12g/620ml catalyst concentration was 91.2%.

Fig 2. Percentage removal of COD as a function

Fig 3. Percentage removal of COD and BOD as a catalyst loading function of time

Effect of different nutrient loading on the COD removal:

The performance of the FICCO reactor was studied with the concentration of anionic surfactants. The average inﬂuent concentration of surfactants was 23.8 mg/L, of which the FICCO reactor removed 80%. The COD and BOD removal efficiencies reached 82.7% and 81.5% respectively which is shown in the graph (Fig. 4), leading to average efﬂuent concentrations of 4.8mg/L. Anionic surfactants are readily biodegradable under aerobic conditions as opposed to anaerobic conditions, at which they are unlikely to be degraded.

When the reactor was operated at suﬃcient aeration condition with the addition of starch, the removal eﬃciencies of COD and BOD reached 88.1% and 87.7% (Fig. 5) respectively. The initial starch content was found to be 32.1mg/L. After 3 hrs of treatment in FICCO reactor the starch content got reduced to 5 mg/L. This clearly shows that the oxidation process in this reactor is capable of reducing the starch content.

The performance of the FICCO reactor was studied with the concentration of adding oil and protein to the waste water in addition to surfactant and starch. The average inﬂuent concentration of oil and protein in the waste water was 45 mg/L and 33.7 mg/L respectively. The average effluent concentrations of oil and protein from FICCO reactor was 6 mg/L and 4.27 mg/L respectively. The maximum COD and BOD removal efficiencies reached 85.2% and 84.1% for effect of oil and 85.5% and 77.1% for effect of protein respectively as shown in the Fig. 6 and Fig. 7.

The sludge production for all the given 4 conditions of adding surfactant, oil, starch and protein are presented in the Table 2. After 6 days of continuous running, the sludge was collected from the reactor and the experiments on sludge characterization were studied.

Fig 4. COD, BOD removal % with addition of

Fig 5. COD, BOD removal % with addition of starch.surfactant

Fig 6. COD, BOD removal % with addition of oil

Fig 7. COD, BOD removal % with addition of prote

Table 2: Sludge characteristics

Parameters	Surfactant	Oil	Protein	Starch
Wet sludge weight (g/ml)	3.551	1.1401	1.2837	3.9356
Dry sludge weight (g/ml)	0.5795	0.4384	0.7186	1.0527
Sludge volume (ml/L)	0.72	0.643	1.21	0.73
Volume of compressed sludge (ml/L)	0.0936	0.257	0.164	0.369
Fixed solids (g/L)	0.048	0.036	0.004	0.057
Specific weight (g/ml)	3.5	1.14	1.28	1.3118
Sludge density (g/ml)	0.0599	0.215	0.0269	0.368
Filter sludge compressed (g/ml)	0.7	0.5384	0.1186	0.85

SUMMARY AND CONCLUSION:

The rice husk based carbon was used as catalyst for the oxidation of organics in wastewater discharged from domestic origin. The rice husk based was efficient enough to reduce COD, BOD by 91.6% and 84% respectively. The consistent removal of pollution parameters was accompanied with the removal of pathogenic and antibiotic resistant bacteria. The sludge production is only 60% of the conventional sewage treatment plant. The investment cost towards Sewage treatment plant by employing rice husk based carbon would be drastically reduced and thereby the operational cost towards electrical energy consumption will also be very much reduced. The reactor C with upper hopper length of 3.5cm is considered to be the desired optimum condition for running the reactor with high COD and BOD removal efficiencies. The outlet of the fluidized reactor was then transferred to the algal pond for further treatment through algal process to make the water suitable for release into the outer environment.

REFERENCES:

1. John L Kennedy, Mohan Das, K, Sekaran.G. Integrated biological and catalytic oxidation of organics/inorganics in tannery wastewater by rice husk based mesoporous activated carbon-Bacillus sp, Journal of Carbon. 42; 2004: 2399-2407.

2. Metcalf and Eddy. Waste Water Engineering Treatment and Reuse. Fourth Edition, Tata McGraw-Hill Publishing Company Limited, New Delhi, India, 2003.

3. Roila T, Kortelainen P, David MB and Makinen I. Humic substances in the global environment and implications for human health. Elsevier, Amsterdam, 1998, 863-868.

Received on 29.08.2013 Accepted on 01.09.2013

Research J. Engineering and Tech. 4(4): Oct.-Dec., 2013 page 226-230