206 Environmental Biotechnology
of treatment. A laboratory prototype treatment was developed for the specific
effluent and was successfully trailed at pilot scale, before subsequently being
further developed and extended to the treatment of biowaste.
Eutrophic fermentation involves rendering the waste into a fine slurry, which
is then contained within a bioreactor (Figure 8.4), aerated by means of bubble
diffusers at the base of the vessel, mixed and heated to around 35◦C. Within
this environment, the input waste breaks down to leave only about 10% of the
original volume as recoverable solids within 35 days. The process liquor itself is
characteristically less strong than for anaerobic digestion and typically contains
only some 6–10% suspended solids. Analysis of this liquid by the Agricultural
Development Advisory Service (ADAS) has indicated that it has some potential
fertiliser use, based on key performance indicators such as nitrogen, phosphorous
and potassium levels, electrical conductivity, generalised nutrient content and
heavy metal residues. The results are shown in full in Tables 8.4 and 8.5.
With a ‘satisfactory’ pH of 6, a ‘low’ BOD of 2790 mg/l, low ammoniacal
nitrogen and the likely slow release of much of the total nitrogen content over
Figure 8.4 EF bioreactor
Table 8.4 EF analysis results (nutrients)
Principal nutrients Units per 1000
gallons∗CommentsNitrogen (ammoniacal) 2 Low
Nitrogen 5 Moderate
Magnesium <1Low
Phosphorus 1 Low
Potassium 6 Moderate
∗Standard UK agricultural measure for fertiliser value.