Chemistry is the high-tech of resource efficiency. Without chemicals, the current level of safe water supply and sustainable wastewater treatment in urban areas cannot be maintained. At Kemira, we believe there are many opportunities for sewage treatment plants to contribute to the circular economy. With a little chemistry, municipalities can turn sludge and other underutilized resources into valuable assets that improve profitability while supporting sustainability.
From nuisance to nutrients
While causing eutrophication of the waterways when in excess, phosphorus is an important fertilizer. The best phosphorus recycling options are manure from animal farms (80%) and phosphorus from wastewater (20%). Manure is already recirculated to a great extent, so more focus is needed on recovery from wastewater. Sewage sludge contains phosphorus, nitrogen, iron, potassium, calcium, and magnesium, as well as other macro and micronutrients. This waste product, which is often viewed as a nuisance by wastewater treatment plants (WWTPs), can be a rich source of organic fertilizer.
The phosphorus in wastewater can be reduced mechanically, chemically, or biologically. Mechanical treatment separates at the most some tens of percent of the incoming phosphorus; only particle-bound phosphorus can be separated. A conventional biological treatment plant can remove 20–30% of the phosphorus from wastewater, whereas chemical treatment can remove more than 95%.
WWTPs can recover phosphorous and essentially recycle this resource by offering it to farmers as an attractive alternative to commercial fertilizers. A 30-year research project in Sweden showed that chemically precipitated sewage sludge increased crop yield by 16% without the use of mineral fertilizers. Recovered phosphorous can also be applied in forestry to recondition soil and improve plant growth.
But WWTPs must be mindful of meeting the safety standards for such applications. Kemira’s solutions can help by removing harmful compounds like toxic metals, organic micropollutants and pathogens. We’re happy to collaborate with customers to explore the best technologies for their specific situation.
Learn more about sludge and fertilizers in Kemira’s Water Handbook.
While phosphorous recovery keeps a natural resource in the value chain longer, there are other ways that sludge can go from zero to hero.
Sludge as a source of sustainable energy
Most people generate about 50 kg of solids for disposal every year. All that waste is a consistent renewable resource. Municipalities can turn sludge and other organic waste into biogas to decrease disposal costs, increase resource efficiency and unlock hidden value.
Here’s how it works. Biogas is the result of degradation of organic matter in anaerobic digesters of a WWTP. Made mainly of methane and carbon dioxide, it is a highly potent and sustainable energy source. Chemical pre-precipitation increases the amount of biogas produced during the anaerobic digestion of sludge. During conventional biological treatment, a large proportion of the particulate organic material is converted to carbon dioxide. But during pre-precipitation the particulate organic material remains intact in the sludge, which means that it can be converted to methane gas in an anaerobic digester. This means that considerably more methane gas is generated when pre-precipitated sludge is digested than is the case with biological sludge. In some cases, plants can generate enough biogas to become self-sufficient from an energy perspective.
Our Water Handbook explains the mechanism behind biogas production at WWTPs and industrial biogas facilities, how to best use different types of organic matter for biogas production, and the role of chemistry in the process.
Chemistry for the circular economy
At Kemira, we’re committed to working with water industry partners to extract maximum value from the least amount of resources and keep them in circulation. Our portfolio of chemical solutions can help you optimize resources, processes, and energy use to support SDG 12.