Two basic ways of biosolids liming were developed and proven (link):
Lime slurry (milk-of-lime) is mixed with biosolids in a liquid –to-liquid way prior to dewatering. This process is particularly suitable for dewatering in filter presses. Mixing is very homogeneous but extra water is added here while the final target is opposite – to minimise the water content.
Quicklime is typically used here; it is mixed with dewatered biosolids in an additional step. Post-liming reduces the water content strongly and provides faster hygienisation. However, the homogeneity is lower and the relative lime dosage is higher compared with pre-liming.
The CODECAL process, developed by Carmeuse, is an effective combination of two main processes mentioned. It uses delayed reactivity quicklime mixed in a pre-liming way.
The CODECAL process benefits are:
- Homogeneous lime mixing with liquid sludge
- Dewatering improvement by flocculation and additional mineral load effects
- Additional drying of dewatered biosolids
- Fast hygienisation comparable with post-liming
- Lowest apparent lime consumption compared with both conventional liming processes
BIOCALCO QD is Carmeuse lime product developed for the CODECAL process. Its alkali reaction occurs immediately after mixing with liquid substance while the exothermic hydration starts as late as after the dewatering step. The delay in exothermic reaction can be customised to a given wastewater plant.