Abstract: The Issue: With the growing interest in Resource Recovery, many biosolids producers are keen to continue to recover the nutrients and organics in their biosolids through land application to agricultural lands. The traditional land application of dewatered biosolids, however, often raises concerns from regulators and the public about odors, dust and nutrient run-off. In addition, newly implemented or soon to be implemented Nutrient Management Regulations in each state will limit how much and where biosolids may be used in agriculture.
The Solution: Over the last 8 years a number of biosolids producers in Canada have made use of a biosolids hydrolysis process to overcome stakeholder concerns. This process produces a high solids EQ biosolids liquid that can be land applied in a way that offers a number of benefits to the ratepayer, the public, environmental regulators, and the farmer.
Meeting Regulatory Requirements: In the United States, farmers are facing challenges due to the Natural Resource Conservation Service (NRCS) Code 590 that requires each state to develop nutrient management standards for agriculture that meet the federal requirements. Code 590 states that: “Nutrients must be applied with the right placement, in the right amount, at the right time, and from the right source to minimize nutrient losses to surface and groundwater.” Nutrient management standards will force farmers to closely manage their tillage practices and choose fertilizers and soil amendments that are less likely to migrate to water bodies. As more farmers favor “no-till” methods of planting crops to help reduce soil compaction issues and improve long term soil health, they are less inclined to participate in dewatered biosolids programs at all. The biosolids hydrolysis process and product may help farmers address these challenges. The process produces a Class A Exceptional Quality (EQ) Canadian Food Inspection Agency registered fertilizer which reduces setbacks and the need for regulatory reporting. This high solids, liquid fertilizer product also meets the requirements for US regulations.
The Process: There have been many papers written about the benefits of biosolids hydrolysis technologies used to create a low odor, EQ product when installed in a pre-digestion configuration. The hydrolysis process can also provide some of the same advantages when installed after digestion and dewatering. This post-digestion, post-dewatering configuration has a very unique benefit over pre-digestion hydrolysis. It produces a high solids (15%) liquid that significantly reduces land application costs over dewatered programs, especially when agricultural lands are within a 40 mile radius.
Benefits: From a ratepayer/cost perspective, many of the wastewater agencies in Canada that are using this hydrolysis process report over a 50% reduction in third party costs to haul and land apply high solids liquid biosolids compared to their dewatered programs.
There are a couple of reasons for this. Liquid land application programs can load a truck much faster and more accurately than dewatered programs and, since a liquid tanker truck is usually lighter than a dump trailer, it can take on a heavier payload. Also, liquid land application programs only require one operator and one piece of equipment in the field, while dewatered programs usually require 2-3 operators and three pieces of equipment. In terms of the process, most wastewater agencies are very comfortable operating and maintaining pumps and piping systems, so it is easy for them to manage a liquid program. A dewatered program, on the other hand, requires conveyors and storage hoppers that often require greater attention of operators and maintenance staff.
Canadian agencies have reported that many farmers are more receptive to biosolids management programs that minimize soil compaction and disturbance and do not require the biosolids to be stockpiled in their fields. The use of a high solids liquid biosolids product is a good solution to these concerns. During land application, the product is immediately injected into the soil in one pass, creating minimal soil disturbance and eliminating any issues with offsite odors, dust or nutrient run-off. There is no need to stockpile the biosolids in the field so this eliminates odors and nutrient run-off concerns. The injection process also minimizes nitrogen volatilization.
From the public’s and regulator’s perspective, the high solids liquid biosolids are fully contained in an enclosed tanker during transportation so there is a never an issue with odors at this time. Full containment also eliminates the risk of a biosolids spill during a sudden braking event.
Since the product is a liquid, it is very easy to add additional nutrients, such as potassium, that will make the product more marketable to the farm community as an alternative to a custom blended chemical fertilizer. New or proposed Nutrient Management Regulations for agriculture strictly limit the amount of N-P-K that may be applied to farm fields. This can be problematic with biosolids products since they usually have more phosphorus than needed when the crop nitrogen demand is met. The high solids liquid product can be custom blended to meet the crop’s proper N-P-K demand.
Additionally, the liquid form allows the material to be applied with precision and at a consistent rate, facilitating better nutrient management. The high solids liquid may be kept in storage and injected at an optimal time when the crops will utilize the nutrients assuring farmers that the nutrients applied to crops are readily available in the root zone when needed. Since the nitrogen is primarily in organic form, it is released gradually to meet the crop demand. Subsurface injection of liquid EQ biosolids also minimizes the nutrient losses due to runoff and volatilization.
When fertilizer is injected, there is a reduced loss of P compared to surface application and conventionally tilled fields. In addition, similar to Enhanced Efficiency Fertilizers, the slow release nature of the N and P reduce the risk of nutrient transport to surface and groundwater and increase availability to the crops. Product marketability is also enhanced when storage and minimum disturbance injection is provided. Given these potential benefits, the NRCS will be paying land owners to use certain Enhanced Efficiency Fertilizers as part of the Conservation Stewardship Program, up to $47/acre. At present, farmers are paying for injection of liquid manure and fertilizers and paying a premium for Enhanced Efficiency Fertilizers. The NRCS-approved nutrient risk assessment for phosphorus (P-Index) must be completed when:“phosphorus application rate exceeds land-grant university fertility rate guidelines for the planned crop(s),”
Proposition: This paper will present data showing how the biosolids hydrolysis process can help farmers comply with nutrient management regulations while reducing land application costs.