Ureka Limited has developed a unique patented solution (Patent number GB 2335188 B) to the major environmental problem affecting developed areas, the commercially beneficial treatment of putrescible organic waste which is currently composted, digested, landfilled or incinerated. The patent not only protects the process but also the unique generic series of products which are manufactured by it.The following is a brief description of the process used to manufacture the new matrix bound organically enriched fertiliser from the organic fraction of MSW. A process flow diagram is shown overleaf.
The base organic material and water are mixed together in a mixer to turn the organic waste into a slurry. The purpose of this initial mixing is to enable tramp material to be easily removed. The dry solids content of this slurry may vary between 3% and 15% depending on the base organic material. After mixing the slurry is emptied from the mixer into a surge tank which is fitted with stirrers to prevent the solids from settling out.
The slurry is screened to remove small bits of plastic, metal or other oversized inorganic matter, to ensure that no tramp material is carried through to the fertiliser production phase. This enhances the quality of the product produced, as the slurry is now virtually free from inorganic contaminants. The organic slurry passes through the mesh and is pumped at a constant rate to the fertiliser plant.
If there are no cheap sources of power and heat near the proposed or preferred site, and/or if the amount of fertiliser produced needs to be reduced because of local market conditions, the organic sludge may be wholly or partially digested to produce biogas and simultaneously reduce the solids content of the sludge.
The digester is maintained at a constant temperature to promote bacterial action. The bacteria break down the solids in the digester and produce biogas which is composed of methane and carbon dioxide. The amount of gas produced and the proportion of solids reduction depends on the digestion period. This gas is drawn off and stored in a buffer store prior to being used to raise steam. The steam is used to generate power to run the plant and heat to dry the fertiliser and to heat the digesters. The digested slurry is pumped from the digesters at a constant rate to the thickener. Alternatively if the digestion phase has been omitted from the overall plant the slurry will be pumped directly from the screens to the thickener.
The purpose of the thickener is to remove excess water and control the moisture content of the material produced before entering the initial reaction phase of the fertiliser process. The excess water from the thickener is pumped away to a settling tank where grit and fines can be settled out and removed, enabling the water to be recirculated through the initial mixer. The resulting organic paste exits the thickener and is conveyed to a surge hopper. The paste at this stage has a moisture content of around 66%, however this percentage can vary depending upon the base organic material being used and the Nitrogen (N), Phosphorous (P) and Potassium (K) values required in the final product.
Acid and ammonia are added to the paste to give the fertiliser the required nitrogen content. The addition of acid and ammonia create heat so that the material reaches temperatures of up to 90OC. This, and the rapid changes of pH, has the effect of pasteurising the material and killing weed seeds and harmful microbes. Phosphate and potash are then added to give the fertiliser the required P2O5 and K2O contents. The addition of these ingredients also results in a dry solids ratio which allows good granulation of the product in the final stage.
The process is designed to compensate for and permit variations in the organic base material and ingredients by being able to adjust the dry solids content of either the incoming slurry or paste. This flexibility in the process allows for the production of dif