Biosolid products contain good quantities of most major plant nutrients, organic matter, and valuable amounts of micro nutrients. The use of the nutrients contained in organic materials such as biosolids is a sustainable way of reducing the amount manufactured fertiliser products used by farmers.
A typical biosolid digested cake (25% dry matter) product applied at a rate of 20 t/ha can provide the following.
* Depending on soil P and K indices and crop being grown.
** Assume 10–20% available following autumn applications and 20% following spring applications.
Quality assurance with HACCP
Southern Water incorporates Hazard Analysis Critical Control Point (HACCP) quality assurance systems within its treatment processes. These systems ensure that the required bacterial standards for biosolid products are guaranteed.
The HACCP system was developed in the food industry to ensure that the required standards at each process stage are continually met. In the UK the same HACCP approach has been adopted by the Water Industry for its treatment of raw sludges to treated biosolids.
Under this system limits are set for factors which are critical to maintaining end product quality. These factors are defined as Critical Control Points (CCPs) under the HACCP system. By operating the treatment process within the CCP limits, the end product quality is assured.