The sludge problem
The percentage of solids contained in wastewater effluent is only 0.1%, and the primary objective of a WWTP is to remove and treat that small percentage of solid waste. Some 40%-50% of these solids undergo biological digestion in the WWTP, and the rest accumulates as sludge.
Sludge is comprised of solid materiel that does not decompose, or decomposes slowly, and in addition contains live and dead bacteria. The particles that barely decompose are mainly cellulose, fats, oils and minerals.
After the screening process in existing WWTP systems, the sludge, referred to at this stage as dry sludge, still contains 80% water. So, every truckload of sludge that is headed to a disposal site or landfill is carrying 80% water and only 20% solids.
Sludge is a huge environmental nuisance and an economic burden. The costs of sludge disposal are exceedingly high, and have been rising steadily over the past several years.
Currently, there is no good solution for reducing sludge volume. The existing solutions are only reusing sludge ineffectively – not reducing it, leaving an intolerable unsolved and growing global problem.