2.7.3. Loading rate
A uniform loading of manure with 6–10% solids on a daily basis generally works well with the load’s retention time in the digester ranging from 15–30 days [52]. An issue with digesters is that blockages can be caused by using waste resources that have a variable solid content. In the case of hatchery waste the content of solids can be variable depending on whether most of the waste comprises mainly non fertile eggs that are removed from the incubators during incubation or if the waste is made up mainly of dead embryos after hatch.
2.7.4. Mixing
The effluent in the digester needs to be mixed regularly to prevent settling and to maintain contact between the bacteria and the manure. The mixing action also prevents the formation of scum and facilitates release of the biogas [52]. In the case of livestock effluent it sometimes contains fibrous materials which can cause blockage in digesters.
2.7.5. Management
Regular monitoring, maintain a constant required temperature of the digester is important if the system is to run smoothly. Failure to properly manage the digester can result in poor gas production and some systems take months to get back into operation if there is a breakdown [52]. Quality control needs to be implanted to manage the waste resources being utlised in the digester as well the biogas and other products being produced. Records need to be maintained on biogas and other products produced and the effluent that has been fed into the system [52].