HOW ARE BIOSOLIDS PRODUCED?
The road from wastewater to biosolids is a long one. The first thing that happens when wastewater enters a treatment facility is screening. In this process, undesirable objects such as plastic, rags, and stringy material are removed and landfilled. After screening, the wastewater undergoes both primary and full secondary treatment; depending upon specific regulatory requirements, some wastewater receives tertiary treatment. During primary treatment, solids are removed by physical means including settling, skimming, and additional screening. The wastewater then moves on to secondary treatment, where microorganisms feed on organic materials in the wastewater in the presence of oxygen. After secondary treatment, we’re left with clean effluent that can safely be discharged to the waterways, and captured solids known as raw sludge. The work is far from over, though. The raw sludge from all treatment stages must be processed further to produce biosolids. The additional processing kills disea
The production of biosolids from the Water Corporation’s metropolitan operations involves the following stages: The first stage in the production process is mechanical screening, followed by settling and skimming for the removal of large floating objects, sand, grit and settleable organic solids. The second stage is a biological breakdown and stabilisation process. Micro-organisms in the wastewater feed on the sewage converting them into the natural, mostly organic solids. At the third stage the collected organic solids from the first and second stages undergo extensive stabilisation by anaerobic (without oxygen) digestion. This process stabilises the organic matter while reducing the quantity of solids and the level of pathogens (disease-causing bacteria). In this process a large amount of organic matter is biologically converted into methane gas that can be used by the treatment facility to generate power or heat for the process. The stabilised solids resulting from the digestion pro
