As we move to a more sustainable future, where each waste stream is seen as a resource, co-digestion will become a vital part of sewage waste management.
Sewage waste treatment produces energy-rich sludge, made up of things like fats, grease and oils (FOG), and food scraps. Using co-digestion (anaerobic digestion of the sludge), FOG and food scraps can be diverted from landfills and sewer lines, and the sludge can be used to produce methane gas — a valuable energy source when fossil fuel supplies are dwindling and power prices keep rising.
Many countries are already using anaerobic digesters to make their waste valuable. The anaerobic digestion will generate methane gas, but it needs a putrescible feedstock. The more putrescible it is, the more methane gas it will yield. Hence Australia’s growing interest in using municipal sewage or septic sludge, which is particularly putrescible! It hits two goals at the same time; finding a use for sewage waste that would go to landfill, and generating a significant amount of methane gas as a renewable source of energy.
If sewage sludge is to be used as a feedstock, physical contamination by non-putrescible stones, wood chips, metals, glass and plastics must be removed by screening. Like many processing plants, screening is a critical pre-treatment stage because not only are the contaminants non-putrescible, they can damage the anaerobic digesters and significantly reduce efficiency.
Another problem in processing sewage sludge is the accumulation of foam and grease waste, which can ultimately clog pipes and pumps. This is a common problem, yet an efficient solution has not previously been available in the market. If not eliminated, these contaminants can block the digesters resulting in inefficient performance, reduced methane production and, of course, a lower profit.
Leading German company HUBER SE has developed an efficient and innovative solution to the problem of accumulated physical contaminants, grease and foams. The HUBER RoFAS is a lightweight wash drum made of stainless steel that separates septic sludge, food sludge and grease trap material from solids ranging in size from three to 100mm.
The internal drum of the HUBER RoFAS can cater for feedstock with a high-solids throughput, even with unusual materials like tree debris, large stones and bricks. The HUBER RoFAS can also lower maintenance costs due to its durability when exposed to a high-solids throughput. The five, ten or 20kl tankers that transport the waste discharge directly into the HUBER RoFAS via a feed manifold. The amount of feedstock discharged from each waste transporter can be measured via the control system.
The HUBER RoFAS will protect digestion processes from any coarse screenings in the feedstocks or sludge streams, reducing digester maintenance and ensuring the digestion process operates at optimum efficiency.
Lauren Butler is the assistant editor for Utility Magazine. She’s based in Melbourne, Australia.