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A hybrid fluidized bed biological reactor was developed for the treatment of diary wastewater. It consists of direct fluidized bed and inverse fluidized bed in the inner core and the annular region respectively under aerobic condition. Ceramic support particles and spherical plastic beads were used for direct and inverse fluidization respectively. The reactor influent was raw distillery wastewater (pH 8, TSS 1600 mg/l, Total dissolved solids 900 mg/l, COD 2000 mg/l, BOD 1200 mg/l). The results show that the percentage reduction in COD is 94.5%. The comparative study has proved that the HBR has a higher efficiency in the treatment of organic loads when compared with the normal fluidized bed reactor. In this novel reactor setup, the active reactor area is increased and there is a decrease in the operating cost as it utilizes the energy supplied for the direct fluidization to the inverse.
KEYWORDS: Dairy waste, fluidized bed bioreactor; Inverse fluidization; biogas.
Rapid growth of industries has not only enhanced the productivity but also resulted in the production and release of toxic substances into the environment, creating health hazards and affected normal operations of flora and fauna. These wastes are potential pollutants when they produce harmful effects on the environment. It has been recognized quite recently that biological systems, primarily of microbial origin could prove potential means of degrading such complex environmental pollutants. Besides, like other industries that have serious waste disposal problems, the dairy and distillery industries are faced with the prospect of having to erect a large number of treatment plants. Liquid effluents from dairy industry cause both water and soil pollution 1.
In the dairy industry, milk, water and detergents are released as a result of routine operations. The nutrients present in the waste water feed algal blooms which then further depletes oxygen thereby causing serious damage to the water course when it is discharged2.In the present work a Hybrid reactor (HBR) was developed and the performance was compared with fluidized bed reactor (FBR) and is used for the treatment of dairy wastewater.
MATERIALS AND METHODS
The principle of fluidization is used in the Hybrid biological reactor for the treatment of dairy wastewater. The reactor setup is shown in the fig 1. The novel bioreactor consists of an inverse fluidized bed in annular region and a direct fluidized bed in the inner core under aerobic condition. Direct fluidization is achieved by pumping the effluent from the bottom of the reactor. The inverse fluidization is achieved by the down flow current of the liquid.
Ceramic support particles of diameter 2mm and bulk density of 1516 kg mâË†'3 were used for direct fluidization and for inverse fluidization, spherical plastic beads of bulk density of 518 kg mâË†'3 and 2 mm diameter and were used. Set up consists of inner direct fluidized core of height 1 m and diameter 50 mm and inverse fluidized core of height 0.6 m and diameter 150 mm and a disengaging section of height 0.6 m and diameter 200 m. The effluent was fed into the column using mono-block pump of 0.5 HP, and the liquid flow rate was controlled by using a rotameter which is of range 0-500 L h-1.The air flowrate was maintained at 40 LPH .
Dairy waste water
The dairy waste water is complex biological fluid consisting of milk fat, protein, lactose and lactic acid, as well as sodium, potassium, calcium and chloride3,4. The dairy effluent was collected from a Dairy & Farm Products (P) Ltd located nearby Thanjavur, and stored in a refrigerator at 19Ã¯â€šÂ°C in order to prevent biodegradation.
Microorganisms were incubated along with the culture media for a few days in order to coat them on the support particles. The effluent was pumped from the bottom of the fluidizing column and the liquid flow rate was monitored. The gas and the liquid streams merged and passed through an expansion cone. The inverse fluidization is achieved by the down flow current of the liquid.
RESULT AND DISCUSSION
The hybrid bioreactor treating diary waste water showed high process stability. The operating cost is low as it utilizes the energy supplied for the direct fluidization to the inverse. Results presented have clearly shown that it is possible to effectively degrade dairy waste water. High surface area of the support particles assure that enough viable biomass inside the reactor is maintained during both direct and inverse fluidization.
A comparative study of hybrid aerobic reactor with equal volume of aerobic fluidized bed reactor for the treatment of dairy wastewater is shown in the Fig.2. Maximum COD removal was seen in hybrid reactor. The hydrodynamic characteristics of the reactor were studied. In case of single phase fluidization, there is an increase in the pressure drop across the bed along with the flow rate. The throughput capacity of the system is increased with the help of low density particles, although in such cases, pressure drops are higher when low density particles are used compared to high density particles 6. The experiments were performed with different initial bed heights of 4, 5, 7 and 9 cm in both direct and inverse bed. COD reduction with respect to different initial bed height and pressure drop in the column is shown in Fig.3. It was found that the percentage reduction in COD increases with increase in bed height. The increase in COD reduction along with bed height was due to increase in volume of biomass support particles7. Increase in bed height in turn results in the increase of the pressure drop in the column. From the Fig. 3 total pressure drop increased from 333.5 N/m2 for 4 cm equal bed height to 655 N/m2 for 9ÂÂ cm column in both inverse and direct fluidization in the column. Hence optimum bed height of 7 cm was chosen for the pilot plant operation.
For dairy effluent, a maximum COD removal efficiency of 94.5% is achieved which is relatively higher than that for normal fluidized bed reactor. Fig 4 represents the % COD removal at various hydraulic retention time (HRT) 8. The COD reduction decreased with HRT. When HRT increases, it would result in the decrease in the wastewater linear velocity through the support. This observation is in good agreement with previous reports9 .When there is an increase in the HRT from 0.5 to 2 h, percentage COD removal increased from 86% to 98%. It is clear that the COD removal efficiencies and especially the methane productions are inferior for the lower HRTs (0.5 and 1 h) than to those obtained with the higher HRT (2 h).
Based on the analysis and interpretation of the experimental results for biodegradation of dairy waste water in HBR the following conclusions were drawn. Results presented in this report have clearly shown that it is possible to degrade effectively dairy waste water containing high organic loads in the novel bioreactor, since operational conditions such as high surface area of the support particles, are assured in order to maintain enough viable biomass inside the reactor during both direct and inverse fluidization. The hydrodynamic characteristics of direct and inverse fluidized bed are experimentally determined. When low density particles are used, there is an increase in the throughput capacity of the system, although higher pressure drops are encountered when compared to the high density particles. There is an increase in the pressure drop with increase in the flow rate and the bed height. The comparative study has proved that the HBR has higher efficiency in treating the organic loads when compared with the conventional fluidized bed reactor. Also the time taken for degradation is less. And hence the novel reactor can be used for the treatment of various other industrial wastes and the efficiencies can be articulated and the Hybrid reactor can be scaled up for industrial applications.