Quds University Small Scale Waste Water Treatment Plants in West ...

Sludge Blanket Unit
This is an anaerobic treatment of the waste. The anaerobic systems use the action of microorganisms
which can survive in absence of dissolved oxygen. The applications concern
the treatment of the organic substance, led by heterotrophic bacteria. Within said
process, the hydrogen removed by enzymatic way links mainly to the oxygen, carbon,
nitrogen and sulphur contained in the organic molecules (Crittenden, 2005)
The chemical reactions which occur within the anaerobic digester produce a series of gases
which are also called biogases: typically methane (70%), CO 2 (25-30%), nitrogen (2-5%)
hydrogen sulphide and hydrogen. Its heating value is approximately 5000 to 6000 Kcal/m³
against 11,000 of the network methane (Crittenden, 2005).In the decomposition process,
the anaerobic reaction is strongly influenced by the temperature and - consequently
- by the availability of the biogas which is used to maintain the ideal conditions.
Furthermore, the operating efficiency is linked to the generation of granular sludge:
every granule consists of a set of anaerobic bacteria which can transform the organic
substances into biogas. Studies developed with the support of the electronic microscope
have revealed some areas within the granule which are specialized in acidification,
methanation of both the fat acids and hydrogen. The generation of sludge during the
anaerobic treatment is very low, since the highest portion of the organic matter
converts into biogas. Furthermore, it can be re-utilized to start new anaerobic reactors, or
used as fertilizer. The management cost of the sludge is therefore minimal. Nevertheless,
this type of treatment is generally less efficient than the aerobic one and -consequently -
it is more commonly applied as a preliminary treatment system, in case of heavily
concentrated wastewater (Crittenden, 2005)
Biodisks
This system is an attached-growth process.
They are disks in high-density laminar polyethylene - whose diameter is generally no
greater than 3.5 m - axially connected by a shaft which is usually no longer than (7.5 m)
and partially submerged in a tank (by approximately 40%). The shaft rotates slowly
(approximately 20 m/min or less) and ensures appropriate oxygenation for the generation of
micro-organisms. As in the case of the trickling filters, the biofilm detaches naturally once it
reaches a significant thickness (Metcalf & Eddy, 1991).
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