The by-product of wastewater treatment – sludge – is considered a problem for most utilities. However, partnership opportunities can be developed that allow private companies to turn that sludge into valuable fertiliser, saving municipalities time and money. 

In many instances, sewage sludge is seen as a low-value waste that needs to be disposed of at the lowest possible rate. Transporting this sludge to be disposed of at a landfill or on agricultural land comes at a significant, ever-increasing cost, as rapid urbanisation continually increases wastewater volumes.

As a result, utilities often seek to dispose of sludge in land applications at the highest possible application rate, as close as possible to the point of generation, complying with the minimum level of compliance possible.

Sludge for agriculture

If correctly treated to A1a requirements, sludge can be hugely beneficial to agricultural land. Biosolids from the wastewater treatment processes consist almost entirely of dead and decomposed microorganisms. Once stabilised and processed, the resultant product is rich in humus and humic substances, as well as plant macro- and micronutrients. 

The organic fertiliser that can be produced offers many measurable, positive effects on crucial soil processes. It improves soil structure through the formation of aggregates, thereby also improving gas exchange and soil permeability. The material retains up to 20 times its own mass in water, preventing drying and shrinking of soils, while also dramatically increasing cation exchange capacity and the formation of chelates.

However, from a nutrient perspective, excessive amounts of biosolids are often applied when municipalities opt for the highest possible application rate as a means of lowering costs. According to Francois Burger, managing director, Agriman, biosolids have far more value if applied at the right rate, in the appropriate relation to other nutrients, and in the right physical format.

Compliance

“Unfortunately for sludge producing authorities, the agricultural industry has developed into a highly scientific environment with the current trend of precision farming practices, which requires any new entrants to the market to provide all the services in the value chain,” says Burger. This includes agronomical advice, evaluation of chemical soil analyses, prescription of fertiliser programmes, formulation and blending of prescribed mixes, after-sales service and problem-solving.

Producers of fertiliser products to be used in agriculture need to comply with legislation (Fertilizers, Farm Feeds, Seeds and Remedies Act (No. 36 of 1947)) as well as standards regarding physical properties – e.g. density, particle size, hardness, chemical stability and flow. To compete in the conventional fertiliser market, the product must be fit to be applied by conventional equipment and implements.

Aiding municipalities

Although sludge is often considered a burden, companies like Agriman partner with municipalities to transform their sludge into fertiliser for the agricultural industry. The products and services developed by Agriman for the beneficial utilisation of wastewater sludge cover the entire value chain, from sludge dewatering right through the process of fertiliser manufacturing and sales, up to after-sales service to the farmer in his fields.

The benefit to the local authority is that they bear no responsibility for the ‘waste’ product once it leaves the gate, as the product becomes a registered fertiliser. They do not incur any transport costs and, due to the value proposition, the distribution radius of the product exceeds the borders of our country. This, says Burger, is a true example of a viable circular economy.

“Municipalities should focus on producing a top-quality sludge, investing in proper on-site dewatering and drying facilities. Then they can pass their sludge on to organisations like Agriman to produce fertiliser products, without incurring the ever-increasing cost of off-site disposal,” he concludes.