Hi Anvar, this is a big ...

Hi Anvar, this is a big question to answer as it depends on several variables.

In essence your sludge strategy and legal compliance commitments need to be considered.

One of the biggest costs associated with sludge management is the transportation cost, whether the sludge is being discarded to landfill (globally being discouraged and/or outlawed), to incineration or transported to land applications (agriculture). From this point of view, volume reduction is paramount. 

To achieve volume reduction, increased volatile solids reduction and dewatering of excess moisture will contribute.

Health risks associated with sludge are high since the digested sludge will still contain ascaris and faecal coliforms as two main pathogens. These should be eliminated to mitigate health and pollution risks

Digested sludge is typically still odorous, by increasing volatile solids reduction, odour can be reduced

By increasing dewaterability and volatile solids reduction, sludge behaviour in terms of stacking, handling etc is improved.

Beneficiated sludge presents huge benefits in land application where carbon, nutrients, microbes will contribute to general soil health and promote fertile soil for crop cultivation

Biogas utilisation form digestion can be utilised and can offset electricity costs by embedding energy through CHP or provided as an alternative to off site LPG use

Adequately applied digestion can have a significant impact on reducing CO2e emissions and reduce GHG's and carbon footprint, across the spheres of wastewater treatment plant site, transportation of solids and application at agriculture site

This has been proven in practice at several established sites applying Thermal Hydrolysis, I know that Thames Water, City of Oslo, United Utilities and DC Water are large entities benefitting from applying Thermal Hydrolysis as an advanced anaerobic digestion step and is worth considering for sites where sludge handling approaches a threshold of probably 50tDS/day and more - economies of scale will influence and so strategy should inform outcomes.

Smaller sludge volumes will most likely still support composting as an alternative, although again a strategy may inform the benefit of regional sludge centres that  can then justify advanced anaerobic digestion.

Bottom line, what does the sludge strategy conclude and what quality of sludge is then best? Capital and operating costs will obviously also influence decision making, with a strategy that identifies drivers and costs helping to determine best fit.

Hope this helps, if you need additional information you are welcome to drop me an email, gary@dikubu.co.za