PROCESS DESCRIPTION :

The vegetable and fruit waste (30 TPD) from fruit and vegetable processing unit is collected in the feed preparation tanks (2 nos) after undergoing weighing and solid size reduction by using a mercerizer and dilution and homogenisation to adjust the solid concentration to the required quantity for the effective biodegradation.

Process water is added to make a feed having 15% solids. The contents are pumped to the bioreactor. Each bioreactor consists of three sections. The effective digestion section is in the middle with biogas section (pocket) at the top and sludge section (pocket) at the bottom having sloping sides.

The digestion takes place in the middle section. Solids are collected in the sludge pocket from where the sludge slurry is sent to the buffer storage tank. The biogas in the top pocket is taken to a gas holder. From here, part of the biogas is sent to the bioreactor for mixing and the balance is then compressed before going to gas engines to generate electricity. The biogas thus generated in the digester is to be stored in a gas tank, which acts as buffer between gas generation and consumption. The biogas does not require cleaning since concentration of hydrogen sulphide is below 1000ppm. The biogas can be used to generate electrical energy by using generator set. The power thus generated is to be put for use in running the biomethanation plant and the excess power shall be exported.

INPUT

Total waste		=  30TPD
Inerts			=  0.24 TPD
TS content			=  7.58 TPD
VS of TS			=  5.6 TPD
Process water added		=  20 TPD
Total Feed into bioreactor	=  49.79 TPD
after inerts removal


COST ANANLYSIS :

Annualised capital cost	=  C [ i(1+i)n]
		     	     i(1+i)n – 1
			=  2.75 [0.135 (1.135)15]
			       [ (1.135)15 -1]
			=  Rs. 43.66 Lacs
			  ( C = Capital Cost = 2.75 Crores,
			   i = rate of Interest = 13.5%,  n = Life of reactor=15 yrs.)


O & M Cost		=  20 Lacs.

Annualised Cost		=  O& M + Annual Capital
			=  20 + 43.66 
			=  63.66 Lacs

RECOVERY :

Biogas produced			= 2520 m3 /day 

Electricity produced			= 225 KWH

Recovery per year			=  225 x 4.5 x 24 x 365
				=  88.695 Lacs.

Compost Produced 4.2 TPD		=  4.2 x 1000  = Rs 4,200 /-
@ Rs.1000 per tonne

Total Recovery per year		=  0.42 + 88695 = 89.115 Lacs.

Payback period			=  Capital cost / (Recovery  –  Annualised cost)
				=  275  / ( 88.115 – 63.66)
				=  10.8 years.

FLOW DIAGRAM FOR A TYPICAL WABIO PROCESS PLANT