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Waste Treatment
• The stable digestate produced by AD is easily converted into a valuable biofertiliser
• AD plants generally have a smaller footprint than aerobic treatment
The HRS DPS ( Digestate Pasteurisation System ) is designed to effectively and efficiently pasteurise digestate , feedstocks , sludge and similar materials . Image courtesy of HRS Heat Exchangers
area for the treatment lagoon ) and untreated biosolids can settle out from the process – requiring further treatment or disposal . The capital investment ( and space ) required for aerobic treatment is usually greater than that needed for anaerobic facilities . While there are pros and cons to both approaches , anaerobic digestion ( AD ) has a number of advantages , including :
• AD is better at dealing with slurries with higher solids content
• AD produces biomethane gas which can be captured and used as a renewable energy source ( including providing the energy to run the AD plant itself )
• AD produces less sludge ( digestate ) for a given volume of wastewater
While the final choice of aerobic or anaerobic wastewater treatment will depend on the unique situation of each treatment facility , the advantages outlined above , together with greater utilisation and uptake of AD technologies including enclosed digesters and upflow anaerobic sludge blanket ( UASB ) systems , means that the use of anaerobic digestion is rapidly increasing in the wastewater sector , either as the main secondary treatment , or to further process the biosolids produced by aerobic processes .
Improving the efficiency of anaerobic digestion As the points above show , one of the major benefits of anaerobic treatment is its improved energy efficiency and the lower volume of residual solids produced as digestate . However , when designing or upgrading an AD plant there are numerous ways to maximise operational efficiency – improving both economic returns and environmental performance . External digester heating ( for example using HRS DTI Series heat exchangers ) offers a number of advantages over heating systems which are located in the digester . External heating can be checked , cleaned or serviced at any time without the need to empty ( or enter ) the digester . Other benefits include the fact that external systems can be designed so that one heat exchanger
24 Heat Exchanger World October 2024 www . heat-exchanger-world . com