Water Resources Research Act Program

Details for Project ID 2016GA364B

Phosphorus and Metal Speciation Dynamics during Thermal Treatment of Sewage Sludges

Institute: Georgia
Year Established: 2016 Start Date: 2016-03-01 End Date: 2017-02-28
Total Federal Funds: $18,000 Total Non-Federal Funds: $36,000

Principal Investigators: Yuanzhi Tang

Project Summary: Tremendous amounts of sewage sludges are being produced as the byproducts of wastewater treatment processes, bringing a daunting task for the water industry. In addition to the intrinsic high water content and large volume, sludges often contain a wide range of organic and inorganic contaminants, such as heavy metals, pesticides, herbicides, microorganisms, and pharmaceuticals and personal care products (PPCPs). On the other hand, sludge also consists of a wide range of nutrients and valuable metals at relatively high concentrations, and is increasingly recognized and treated as a resource for the recycling of critical nutrients such as phosphorus (P). In fact, a significant portion of P consumed by human activities is ultimately converged into wastewater treatment plants, making the sludges a great resource for P recycling and reclamation. For example, the activated sludge and anaerobically digested sludges collected from a local wastewater treatment plant (F. Wayne Hill Water Resources Center, Gwinnett County, Atlanta, GA) contain 3–4 wt% P and has great potential for P recycling. In recent years, thermal (e.g. pyrolysis) and hydrothermal treatments (e.g. hydrothermal carbonization; HTC) of sewage sludge have emerged as sustainable treatment techniques, because they can significantly decompose organic pollutants, reduce waste volume, and generate valuable by-products (e.g. chars). During the production of chars, nutrients such as P mostly remain in the solid phase, making it a char-P composite with many potential applications, e.g. P recycling using acid extraction. (Bio)chars produced from thermal treatments have also been recognized as good soil amendments to adjust soil physical and chemical properties and improve soil qualities. With the significant decomposition of organic contaminants during thermal treatment processes, direct soil application of such char-P composite might also be an excellent alternative P recycling and fertilization practice with all the added benefits from chars. It is well known that the speciation of an element determines its mobility, transport, fate, and bioavailability. Thus, one critical knowledge gap for the abovementioned or any other P recycling/reclamation approaches from thermal treatment derived sludge products is the evolution of P and metal speciation during the thermal treatments, as this relates to the selection of further P recycling techniques as well as the toxicity and bioavailability of metals. In collaboration with Gwinnett County Water Resources Center, this proposed research will systematically characterized P and metal speciation in raw sludges (activated and anaerobically digested) as well as the pyro- and hydrochars derived from pyrolysis and hydrothermal carbonization (HTC) treatments of the sludges under varied treatment conditions. This proposed research will combine a variety of complementary chemical, spectroscopy, and microscopy methods to directly probe the P and metal speciation in the feedstock and the derived chars. Results from this study will shed light on the relatively mobility and bioavailability of P and metals, and provide critical knowledge basis for the potential application of (hydro)thermal treatments for sludge management and nutrient recycling/reclamation. Such information is not only useful for the local wastewater treatment plant, but also directly applicable to any other wastewater treatment facilities.