Wastewater biosolids are considered a product of waste management and the focused has on its disposal, the minimization of the volume, and the application on lands that need nutrient-rich organic fertilizers.
But the rising cost of energy has shifted the focus on sustainability, lower carbon footprint, and independent utilities that could supply renewable sources of energy. There is an increasing interest in recovering the energy that’s inherently available in biosolids.
Fortunately, technology can now transform and convert traditional wastewater plants into resource recovery plants. This is done through the recovery of phosphorus and energy from biosolids.
Eventually, the goal is to establish energy-nutrient plants. There are two pathways that will be able to convert biosolids into renewable energy: through biogas generation and through combustion processes.
The digestion process generates what is called the biogas. This can be used as a source of biogenic energy for process heating and for conversion to electricity. For many years, Europe has been a leader in implementing electric generation through biogas.
North America has followed suit in recent years with many private companies and government-run plants turning away from simple wastewater management facilities and turning these factories into biosolids energy-generation plants. This process could increase renewable energy by as much as 30% to 50%, depending on the solids pre-treatment process implemented.
Thermal conversion can also be used to recover energy directly from biosolids. This is an efficient method to use if you want to tap the renewable energy capacity of biosolids because it allows the recovery, as well as the maximum mass reduction that produces an inert residue, which is ash.
There is another more popular process of disposal being used for biosolids that could also be used to convert heat into energy. Incineration has long been used for volume minimization. The process actually produces excess heat, which can be converted to energy by using steam turbines. Gasification and pyrolysis, both emerging viable bioenergy technologies, also produce energy through modified combustion processes.
Wastewater treatment facilities and plants usually do preliminary testing of these technologies by converting energy that could be used to power the plants. If the process and the technology are both effective, they can now move to transform the facilities into biosolids-generation plants, the output of which could be turned into renewable energy.
Of course, all these processes are regulated and guidelines must be followed thoroughly before conversions can happen.