BIOMETHANATION PLANT BASED ON TAPIOCA PROCESSING INDUSTRY WASTEWATER AT PAPPIREDDIPATTY, TAMIL NADU

BACKGROUND

Tapioca (Manihot Esculenta Crantz) is a crop of great economic importance, both as human food, animal feed as well as raw material for industrial products. In India, Tapioca is grown over an area of about 3 lakh hectares, with a production of 58 to 68 lakh tonnes of tubers. Tamil Nadu ranks second in terms of cultivation and production of tapioca after Kerala but it stands first in respect of processing of tapioca into sago and starch throughout the country meeting about 80 % of country's demand. There are about one thousand sago & starch industries in small - scale sector scattered throughout the State of which 800 units are located in and around Salem district. About 3 cubic metre of wastewater is generated for processing one tonne of tubers, which contains high pollution load, and has to be treated to meet pollution norms set-up by the State Pollution Control Board. At present, there are more than 100 units producing biogas using Tarpaulin cover over the conventional anaerobic lagoons and utilizing the biogas produced for roasting of sago and / or for generation of electrical energy.

The wastewater of about 1200 m3 / day generated in processing of tapioca tubers for production of starch at M/s Varalaxmi Starch Industries Ltd., (VSIL) was therefore utilized for generation of about 0.5 MW of electricity. The raw wastewater contains biodegradable matter such as (i) immature / partially matured starch; (ii) water from tapioca tubers as 55-60% of its weight is water only; and (iii) mechanically un-extractable starch which is 1-2 % of the total starch present in the tubers.

Hybrid Upward Flow Sludge Media Anaerobic Reactor (HUSMAR)

The plant consists of two HUMSAR with 16.5 m diameter and 11.5 m height. In the central part of HUSMAR, Cross Flow Media (CFM) is filled to a height of 4.8 m between two concrete beams. The top pf HUSMAR tank is covered with a floating inverted tank to collect the biogas. The cross flow media has been made of corrugated PVC sheets of 0.7 to 0.3mm thickness, 60 mm plute corrugated angle, bonded together in rectangular modules of size 1.2 m x 0.6 m x 0.6 m providing with a surface area of 102sq metre per cubic metre.

Each HUSMAR is provided with following sensors:

• Flow
  
• pH
  
• Pressure
  
• Gas totalizors
  
• Temperature

The entire plant is controlled by SCADA system.

Wastewater from the equalization tank is pumped into two anaerobic digesters operating in parallel. However, before reaching the anaerobic digesters, the wastewater is mixed with chemicals to improve the pH and also C: N ratio. About 85% of influent BOD is removed in these digesters. The cross flow media provides more space for the growth of bacteria and helps in reducing the HRT to two days and to increase the solid retention time. The wastewater is recycled for efficient gas generation.

Biogas Storage

The biogas produced as a result of stabilization of the wastewater, leaves the digesters and is collected under a negative pressure through gas collection header at the top of the reactor. The biogas consists of 60-65% methane and 35-40% carbon dioxide.

Effluent Treatment Plant

Effluent from the two anaerobic digesters flow by gravity into two aerobic sludge tanks which are capable of removing > 90% of influent BOD from the effluent from the digesters.

Effluent from the sludge tanks is then taken to a secondary clarifier where final clarification of the wastewater occurs and the final BOD concentration in the wastewater is > 35 mg/l.

PROJECT COST

Total cost of the project is Rs. 3.59 crores.

TECHNOLOGY INVOLVED

HUSMAR Technology has been developed at NJIT, New York, USA.

MATERIAL BALANCE

Wastewater feed: 1200m3 / day

ENERGY BALANCE

MANPOWER REQUIREMENT FOR PLANT

BENEFITS ACHIEVED

• Reduction in emission of green house gases
  
• Employment generation
  
• Fuel Savings
  
• Effective waste Management (cleanliness)