Grantee Research Project Results

Project Summary: Phosphorus is a nutrient essential to modern food production and to all life on earth, yet phosphate rock from which phosphate fertilizer is produced is a finite resource, which is rapidly being depleted. At the same time, excess phosphorus from wastewater treatment plants (WWTPs) and runoff from farms is causing eutrophication and the resultant degradation water quality. There is a critical need for technologies and management practices that will recover and reuse more phosphorus for beneficial use in agricultural production. The technology proposed in this research project will exploit the growth of phosphate accumulating microorganisms (PAOs) within an aerobic granular sludge through innovative modifications to existing sequencing batch reactor (SBR) wastewater treatment plant designs. The PAOs, which are growing in the granules, have an active phosphate uptake and release mechanism. The proposed technology manages the phosphate release into the bulk liquid at an appropriate time so that the phosphorus can be stripped from the system to produce a high-value fertilizer product known as struvite. These aerobic granular sludge particles consist of self-assembling microbial communities that form naturally in an activated sludge reactor when the right selective pressures are applied to the system.

 

Project team members have produced aerobic granules in laboratory reactors and the selective conditions which favor the growth of granules over floc-forming bacteria have been identified. A European wastewater equipment supplier has installed at least two full-scale aerobic granular sludge systems in Europe, but their process requires specific basin geometries and proprietary components, which could not be readily adapted to most existing SBR plant designs. The technology presented in this proposal will vastly increase the opportunity for phosphorus recovery by addressing the needs of smaller size facilities with particular emphasis on SBRs, of which there are currently over 700 plants in the United States alone. The total number of municipal WWTPs in the U.S. is about 16,000. Many of these would also be candidates for the proposed technology as they need to be upgraded to meet new more stringent effluent nutrient discharge requirements. Representatives of some major wastewater treatment equipment manufacturers have expressed interest in the technology and would be the natural commercialization partners and investors.

 

Environment benefits: In terms of the life cycle assessment for the proposed innovation, the positive environmental impacts greatly outweigh the negative impacts. The positives include the recovery of a valuable non-renewable resource (P) from wastewater; reduced discharge of phosphorus and nitrogen to ground and surface water, eliminating or reducing the use of chemicals for phosphorus removal; up to 30 percent reduction in the amount of energy used for aeration, thereby reducing off-site greenhouse gas (GHG) emissions from power generation; and less recycle flows due to the compact treatment facilities, thereby reducing energy and space requirements. The negative impacts include those inherent in the construction and operation of wastewater treatment facilities, although these impacts would be considerably reduced as compared to conventional plant designs. Furthermore, in many cases, the proposed technology could be used in existing tanks with only minor modification, and the costs for construction of new tanks to accommodate future growth might be avoided or substantially delayed as the granular sludge also increases the system biomass concentration and treatment capacity. The proposed innovative treatment process application, will provide for the recovery of struvite, a slow-release source of phosphorus, magnesium and nitrogen. Based on its low inherent water solubility, the nutrients are gradually dissolved and available to crops over an extended period of time. Because of these properties, struvite can be applied directly to the plant root zone without causing fertilizer burn, and thus achieve plant yields equivalent to broadcast commercial phosphate fertilizer using as little as one-quarter the application rates.

 

Basic Market Research: In the market for wastewater treatment process technologies, buyers are driven by regulatory requirements, capital cost savings, and operational cost savings. Nearly every State has nutrient-related pollution with impacts in over 80 estuaries/bays, and thousands of rivers, streams and lakes. More stringent permit limits for effluent nutrient concentrations from WWTPs are becoming more frequent in efforts to minimize and prevent water quality impairment from eutrophication. Most of the SBRs in the U.S. have been provided as process equipment packages comprised of aeration and mixing equipment, decanters and proprietary control systems. Many of these systems have performed poorly.

 

This process offers a dramatically improved system with increased treatment capacity for the relatively low cost of a retrofit. The value that dTEC Systems offers to small municipalities experiencing operational difficulties and/or new regulatory requirements is the ability to meet these needs by upgrading existing facilities at a modest cost, rather than constructing new facilities costing several million dollars.

 

Technical Concepts Supporting Feasibility: Granular aerobic biomass has extremely good settling properties and enables much higher biomass concentrations to be maintained in the process, thereby increasing existing plant capacity and reducing the size and cost of new facilities. This has been well established by project team members and other researchers in recent years. Granular sludge selection properties will be applied in a pilot-scale reactor in this research to produce a dense microbial granule with phosphorus and nitrogen removal capability. Tools that are now available will be used in this research to characterize the granular sludge morphology and microbial composition to provide a better understanding of how operating conditions affect the granular sludge size and characteristics. Since the density of granules is only slightly different from water, changes in the density of the water and granules will in itself have a significant impact on the settling behavior of granules. In addition, the granule size influences the settling velocity and therefore both parameters will be monitored in this research. The pilot-scale reactors will be designed to provide the flexibility to adjust each of the important operating conditions that influence the selection of aerobic granular sludge. The flexible reactor design used together with the available characterization tools provide a high level of confidence that the project’s technical objectives can be met. Phosphate release rates of the PAO-containing granules will provide essential information for full-scale design of a struvite fertilizer recovery system.

 

How Proposed Technology Would Outperform Currently-Used Technologies: Currently used technologies include conventional multi-stage biological phosphorus and nitrogen removal treatment facilities. The proposed technology utilizes up to 30 percent less energy for aeration, requires less than half of the space, and uses the available carbon sources in the influent wastewater, which is essential to remove nitrogen and phosphorus more efficiently, thereby reducing or eliminating the need for costly supplemental carbon sources. Furthermore, conventional nutrient removal plants require anaerobic digestion in order to make phosphorus recovery economically feasible. The majority of smaller treatment plants, which includes most of the SBR facilities, do not have anaerobic digesters. The proposed technology does not require anaerobic digestion, and therefore makes cost-effective phosphorus removal and recovery more widely available. Coupled with the fact that many SBRs have failed to meet their performance objectives due to poor settling properties of the flocculant sludge and unreliable phosphorus removal, it will easily be demonstrated that the proposed technology will dramatically outperform these currently used technologies. Where phosphorus limits have been imposed, many small plants have had no option but to use chemical precipitation with metal salts to meet these limits. This is an unsustainable practice, which increases global impacts and makes phosphorus recovery for beneficial use for all practical purposes impossible.