While systems vary in waste solids makeup and improved solids digestion is possible if there is a limiting factor such as:
- Insufficient mixing
- Missing micronutrients (usually in anaerobic systems with low methane production)
- Temperatures are too low (again usually related to methane production)
- Readily Digested Organics - usually dead microbial cells, adsorbed isoluble organics (fats, oils, grease), cellulosics - or the difference between BOD20 and BOD5.
- Slowly Digested Organics - More complex natural polymers, longer chain hydrocarbons, and fatty acids
- Recalcitrant Organics - this includes lignins, complex poly aromatic hydrocarbons, asphaltines, chlorinated hydrocarbons
- Insoluble Inorganics - usually silt, sand, gravel
Usually we can only improve degradation rates of Readily Digested and Slowly Digested fractions. With more complex treatment (getting everything correct), it is possible to remove recalcitrant organics but this takes time and effort. And, the inorganic/insoluble fraction must be removed as it will only accumulate in the system.
So, no matter what you do - wasting or removing solids is necessary. You can only enhance digestion rates and the impact of enhancements depends upon sludge makeup.