Vermiculture in Egypt: - FAO - Regional Office for the Near East and

properties of the treated sludge, the microbial community in the biofilm, and the
earthworm–microorganism interactions in the vermifilter reactor. The results of this
study provide useful information regarding the use of a vermifilter for the optimal
sewage sludge treatment. A cylinder shaped vermifilter (30 cm in diameter and 60 cm
in depth) that was naturally ventilated was equipped with a 0.5-inch polypropylene
pipe with holes to ensure uniform distribution of the influent (Figure 7.3). The
vermifilter contained a 0.5 m filter bed of ceramic pellets (6–9 mm in diameter). A
layer of plastic fiber was placed on the top of the filter bed to avoid direct hydraulic
impact on the earthworms and to ensure an even influent distribution. The influent
sludge was introduced to the vermifilter via a peristaltic pump. After passing through
the filter bed, the treated sludge entered into a sedimentation tank below the
vermifilter and the supernatant in the sedimentation tank was recycled.
Figure 7.3. Layout of the Vermifilter
Source: Zhaoa et al. (2010).
The vermifilter may be an efficient technology for stabilization of excess sludge from
domestic Waste Water Treatment Plants. The volatile suspended solids (VSS)
reduction in the VF reached 56.2–66.6%, which met the criteria for aerobic and
anaerobic sludge stabilization (>40%). The presence of the earthworms in the VF
induced an additional 25.1% reduction in volatile suspended solids. On average, the
earthworm–microorganism interactions were responsible for approximately 46% of
the improvement in the VSS reduction. Moreover, a detailed characterization of
sludge and earthworm cast samples revealed that earthworms in the VF improved the
microbial activity by transforming insoluble organic materials into a soluble form and
selectively digesting the sludge particles of 10–200 μm to finer particles of 0–2 μm,
while enhancing the bacterial diversity in the biofilm. Additionally, improved sludge
settleability with a compact structure and low SVI values (33–45 mL/g) were
achieved in the presence of earthworms, which was favorable for further sludge
processing (Zhaoa et al., 2010).
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