Land-Applied Septage: A Look Into the Future

It’s time to break out of the ‘disposal’ mentality and look at septage as a resource that is beneficial if managed appropriately.

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In the United States, more than 20 million housing units are served by onsite wastewater treatment systems, each with a septic tank.

Within the tank, the accumulation of solids is faster than digestion, and thus the slurry within the tank must be removed periodically. The volume of septage generated by these systems is significant, and this material must be properly managed.

Land application and transport to an approved treatment facility are the most common means of managing septage, and both methods have benefits and drawbacks. Many smaller wastewater treatment plants have stopped receiving septage because it upsets their processes and makes it difficult for them to meet their discharge limits. This forces transporters to travel to the larger, regional treatment plants. The added cost adds to the price of pumping and can become a significant burden on homeowners.

Land-based septage application has been used for generations, but as people occupy what was once remote farmland, there is increased resistance to developing new land application sites. Land application is a viable and sustainable septage management method, but its acceptance requires a change in thinking. Most regulatory documents use the phrase "septage disposal." If land application is to be sustainable, septage must be recognized as a resource and managed appropriately.

Different from biosolids

In 1991, the U.S. EPA promulgated 40 CFR Part 503 to set a national standard for the management and treatment of sewage sludge (now known as biosolids). This same rule considers domestic septage to be sewage sludge and sets separate requirements for its handling and treatment.

Domestic septage is defined as liquid or solid material removed from a septic tank, cesspool, portable toilet, type-III marine sanitation device or a similar system. To handle septage separately from biosolids, haulers must meet at least eight requirements.

First, the land applier must ensure that the septage is only from domestic sources (no commercial or industrial sources). Second, material can be applied only on sites to which the public does not have access. Third, the land applier must manage the application to reduce pathogens. Fourth, appliers must make the application area less attractive to vectors – insects and rodents that could transmit diseases.

Fifth, the owner of the application site must observe crop harvesting, animal grazing and site access restrictions. Sixth, the owner must certify that the pathogen and vector reduction activities are being met. Seventh, the amount of nitrogen applied may not be more than is needed to supply the crop. Eighth, all applicable state and local rules must be followed.

Within these rules, there is a strong notion of using the land to dispose of the septage rather than using the septage to benefit the land. Under vector attraction reduction, for example, a land applier could inject septage below the soil surface, plow the material under, or use lime to raise the septage pH to 12.

Raising the pH is easy, but continuous application of alkaline materials at the same location can increase the soil pH, limiting soil productivity. Of course, tillage practices are also problematic: Tilled soil is highly erosive during storms and the runoff can transport soil, pathogens and nutrients to waterways.

In order to be sustainable, septage application must be synchronized with the natural cycles of the land: Applied nutrients must be harvested with the crop or immobilized in the soil.

Nutrient management

While we rarely use the term "manure" when discussing human wastes, land appliers of septage are in the manure management business. Those who manage livestock wastes from concentrated animal feeding operations (CAFOs) have the same issues of nutrients, pathogens and odors.

To reduce public and environmental health risk from the land application of livestock wastes, the U.S. Department of Agriculture National Resources Conservation Service (NRCS) developed Conservation Practice Standard 590 – Nutrient Management.

Nutrient management focuses on the soil system and how waste materials can benefit the soil and improve crop productivity. A comprehensive nutrient management plan (CNMP) balances the needs of the crop with the nutrients in the septage and the nutrients already in the soil.

The bad news is that most crops do not consume much phosphorus, and as such, phosphorus often limits the septage application rate. A different way of thinking is to grow a crop for the specific purpose of withdrawing the nutrients.

It is important to note that crops with greater biomass yields will remove more nutrients. This is an opportunity: Some types of biomass can be converted into ethanol. Using the plant matter for ethanol production removes nutrients from the land application area and converts them to animal feed (residuals from the biomass conversion).

Continuing challenge

Management of septage will continue to be a challenge for all communities. Regardless of the management option selected, septage management programs must be permitted by appropriate regulatory agencies. Sustainability is more than just a buzzword – it is the new reality. Land application of septage can be a sustainable practice if all the elements are in balance.



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