Ultimate Sustainability – RMV-II with Anaerobic Digestion

The decentralized processing and recycling system based on compost and 100% recovery shows a small promise of profitability in an enterprise mode assuming this is carried out on a soft lease basis (no land costs).  It is obvious that it is economic only at 100% recovery and this may be difficult to achieve.  There is clearly a need for another source of revenue generation to make the enterprise profitable.  Thus instead of aerobic composting the organic fraction (leading to only one saleable product – compost), it is proposed to convert it to biogas and compost (two saleable products) by installing a biomethanation plant of the CST design – similar to the one successfully operated for over 5 years in Siraguppa (Rahman et al, 2009).  In this scenario, the extent of recyclables recovered and earnings accrued does not change from the previous scenario, the income from collection fees also remains the same.  The various costs and returns on investment are worked out for a decentralized waste management with a biomethanation plant as the as given in Table 6.   In this scenario, it is clear that under ideal situation of 100% recovery of recyclables, collection costs and biogas and compost revenues, the pay back period is only 2 years.  Even under an 80% recovery situation, the viability is good.

The costs are calculated at a labour cost of Rs100/head per day (Bangalore rates) and a compost sale at Rs3000/t.  In small towns these are different.  The labour costs are lower (Rs 60), the collection fee could only be about Rs20/HH, the compost revenues are lower at Rs 2000/t and biogas value would be 20% lower.  Similarly recyclables will also fetch a lower value.  Thus when all the incomes from this system is lowered by 20% and compost value chosen at Rs2000/t and daily wage at Rs60/d, the biomethanation option is still viable (Table 7).  This suggests that in a practical scenario biomethanation plant option is more economic and less sensitive to risks in comparison to aerobic compost plant.  Along with economic sustainability, biomethanation options have many other livelihood options (Chanakya et al, 2009; not discussed here).  Composting process also requires continuous use of water of around 200-300 litres per ton of waste (Patel, 2003), which limited its use in dry area or in water scarce city like Bangalore.  Daily collection of fermentables and its rapid feeding into the biomethanation plant overcomes and avoids the smell and insects, rat and dog problems.  Biogas plant and composting bed give same quantity of compost, while compost beds take two to three months whereas in biomethanation plant it takes shorter period of 30d to decompose.  The footprint would then be smaller.  The enterprise could also claim C-credits (CERs) which become yet another source of revenues.  Finally, it may be seen that the operation costs are high due to high involvement of labour.  A major part of the labour is involved in segregation.  As residents become aware and stakeholders the segregation needs would be low and labour deployment could be reduced by about 40% making the system even more profitable.  In Bangalore, where demand of anaerobic compost is high, biomethanation would be a viable process with a pay back period as short as 2 years under ideal conditions and as much as 5 years under less ideal conditions.   The advantage of biomethanation is even more pronounced in small towns where revenue streams from compost and recycling will be thinner.  We thus show that biomethanation based decentralized system is ideal for Indian conditions for making decentralized MSW processing and treatment economically viable and sustainable in the long run.