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Biofertilizer storage

For saving fertilizing qualities of the digested manure, i.e. for preserving nitrogen content it can be stored during a short period of time in a closed vessel and then has to be applied to soil. It is preferable to plough up the soil after application of biofertilizer . Biofertilizer storage is normally accomplished in one of the following forms:
• Liquid storage;
• drying;
• composting.

Liquid storage
Outlet pipe of the biogas system leads directly to the storage vessel. Loss of liquid on account of evaporation or leakage have to be prevented. Before applying to soils the content of the vessel has to be agitated and then applied with the help of spreader or through watering system. The main advantage of this method lies in the small nitrogen losses.
On the other hand the vessel requires big investment and there is a necessity of acquiring transport to transfer the fertilizer to fields. Volume of work depends also on the distance on which the fertilizer has to be transported.

Drying of the biofertilizer is possible in dry and hot weather. The main advantage of this method of storage lies in the decrease in volume and weight of the fertilizer. Dry biofertilizer can also be distributed manually. The cost of constructing small drying vessels is relatively small, but the fertilizer looses around 90% of inorganic nitrogen which constitutes around 50% of overall nitrogen content [8].
In industrialized countries, the slurry is usually separated by means of separators and sieves. The water is re-fed into the digestion process or distributed as liquid manure while the moist sludge is dried or composted.
As a simple technology for separation, slow sand-filters can be used. The moist sludge can be heaped on drying beds, filled in flat pits or simply placed on paved surfaces near the biogas plant for drying. Depending on climatic conditions, large drying areas may be necessary. Drying times and nutrient losses can be reduced by mixing dry substances with the moist sludge. A disadvantage of all drying methods, again depending on the climate, is the high loss of nutrients. Therefore drying of the moist sludge can only be recommended where long distances and difficult terrain hampers transport to the fields or if composting is difficult for lack of manpower and lack of dry biomass.

Nitrogen losses can be minimized through mixing of the digested slurry with vegetation wastes and composting it. Biofertilizer contains nitrogen, phosphorus and other useful components and quickens composting process. Moreover the high temperature of composting kills pathogenic micro flora that has survived digesting in biogas plants. Ready compost, soft and moist can be applied to fields with help of simple equipment and it is easier to transport.
Dry plant material is heaped in rows and the liquid slurry is poured over the rows. Ideally, plant material and slurry are mixed. The mixing ratio depends on the dry matter content of plant material and slurry. The main advantage is the low nutrient loss. Compost, containing plant nutrients in a mainly biologically fixed form, is a fertilizer with long-term effects. It’s value for improving soil structure is an additional positive effect of importance [8].