August 2005 – In most countries, an increasing number of restrictions are
placed on the conventional method of disposing of manure, i.e. spreading it
onto fields and meadows. For this reason, more and more pig manure disposal
plants consisting of mechanical preseparation, acidification, evaporation and
drying systems are built. The energy required for the operation of these plants
is provided by decentralized cogeneration plants. Electrical energy is produced
from natural gas by means of gas engines. The waste heat produced during this
process is used as energy source for the evaporation and drying processes.
This type of disposal involves new waste water streams, i.e. mainly the
condensate from the evaporation plant. For example during the treatment of 15
tons/hr of pig raw manure, about 0.7 tons/hr of dried fertilizer and about 12.6
tons/hr of condensate by-product are produced. Normally the condensate is very
much organically contaminated.
Proven processes for the treatment of the
highly organically contaminated condensate are: biological waste water
treatment, oxidative processes or membrane processes.
GEA Wiegand has developed a new method for solving this problem: the
so-called integrated alkaline vapour scrubbing process. It has been tested on a
pilot scale especially for manure evaporation plants and is being implemented
on an industrial scale at the moment.
By integrating an alkaline vapour
scrubbing system into a raw manure plant, the COD load of the condensate can be
reduced by about 95 %. The following operation has been tested in the plant:
The slightly acidified and mechanically preseparated raw manure is concentrated
in a forced circulation evaporator. The vapours produced are scrubbed in a
vapour column or a packing by means of an alkaline medium. The cleaned vapours
are condensed with cooling water in a surface condenser and are discharged.
The process can be also applied to other types of waste water, e.g.
fermentation substrates from methanization plants for food waste, green
cuttings etc.
Comparisons show that the GEA Wiegand process of alkaline
vapour scrubbing has good chances on the market. The advantages consist in low
investment costs, low operating costs, a high plant safety and good COD
reduction results. The integration of an alkaline vapour scrubbing system into
an evaporation plant for organically contaminated waste water saves the
otherwise necessary additional treatment steps of condensate polishing.