Environmental engineering’s agency Colsen b.v. developed with the Ghent University, the University of Copenhagen and other participants in Europe and Israel a cost effective method to treat manure of intensive stock farming.
The technique uses thermophilic digestion originated from Denmark, the technology of nitrogen and phosphorus removal developed by Colsen b.v. for industrial wastewater treatment and the implementation of bio-membrane techniques.
The thermophilic digester is designed to fulfil thermal conditioning. The digester has a retention time of 25 days a COD yield performance of over 75 %. The digestate is separated in a compost- and a liquid fraction. The liquid fraction is treated in a mesophilic UASB-reactor (post digestion). With this concept over 0,30 Nm3 CH4 per kg organic dry matter is produced.
The compost fraction, to be discharged from the system, is less than 10% of the infeed.
The compost contains a dry matter content of over 35%.
High concentrations of ammonia, present in the liquid fraction of the digestate, are treated in the NAS® (New Activated Sludge) system. The NAS® installation is often designed as MBR (Membrane Bio Reactor) due to the high sludge/water separation performance the membranes and also the possibility to reduce the volume of the system (compact design).
The treated water can directly be of use in the fields as water for irrigation or as water supply for greenhouses.
Discharging the water to surrounding surface water is possible with additional treatment regarding nitrogen, phosphorus and humic acids (adjusted to the local situation).
The feasibility of the manure treatment depends and relies on the energy produced from the recipe of manure and co-products. A very wide range of co-products can be used. The high performance of the digester and UASB-reactor results in the maximum profits from manure treatment.
The (transportation)costs for discharging the compost are minimized due to the high dry matter content of the product. The product can gain some extra profits depending on the local situation.
The costs for treatment of the liquid fraction are caused by the energy requirements for aeration. Due to the high [performance (conversion) of the digester and the enhanced nitrogen removal over nitrite, the energy requirements are reduced as far as currently possible. The digestate treatment produces no additional volumes of sludge, or any by-products resulting in additional costs.
The total energy consumption of the plant is 15 – 25 % of the electrical energy produced.
Manure treatment with this system has an added value regarding energy production and cost effective sustainable treatment of the digestate. A side effect of these developments could justify the expansion of intensive stock farming.
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