Wastewater Treatment of Liquid Digestate from Anaerobic Digestion Plants
- Treatment of liquid digestate from anaerobic digestion plants
- Available for any form of digestate material
- Bespoke design for site specific digestate wastewaters
- Solutions allow for effluent discharge to public sewer or watercourse
- Digestate concentrate suitable for reuse as fertilizer
- Can be designed to meet any specific effluent standard
- Compact and energy efficient
- Reliable processes
- Advanced treatment technologies
- Independently tested
- Low running costs
- Global reference projects
- Contact us for information, advice or a free quotation and design proposal
Our industrial wastewater treatment systems are an ideal solution for the treatment of liquid digestate prior to discharge. We design treatment systems to suit any form of digestate liquid waste. It should be noted that liquid digestate wastewater treatment requires specialist input at design stage. We provide bespoke industrial sewage treatment plant solutions to suit any available space and to meet any effluent standards. When it comes to the treatment of liquid digestate wastewaters, some key factors need careful consideration. Continue reading to find out how we account for them with our bespoke treatment systems and solutions.
Composition of Digestate Wastewaters
Digestate is produced when biodegradable materials such agricultural waste and food waste are processed at an anaerobic digestion plant. Digestate contains all the nitrogen, phosphorus and potassium present in the original material and has value as an organic fertiliser.
The digestate liquid will usually require a form of treatment, particularly nitrogen removal, before it can be discharged to a watercourse or public sewer. When digestate liquid is applied to land as a fertiliser, excess nitrogen can cause environmental problems. Treatment involves the removal or recovery of nutrients by various methods, some of which we will discuss below.
Treatment Stages of Digestate Wastewater
There are various stages in the treatment of digestate liquid wastewater. The methodology largely depends on the composition of the digestate and site specific requirements. The exact composition depends on the material originally processed by the anaerobic digestion plant.
There are various methods available to separate the solid and liquid fractions of digestate, for example drum filters, screw presses, filter belt presses and centrifuges. Dewatering or thickening describes the separation of the solid and liquid parts of the digestate into a fibre (dewatered cake) and a liquid (digestate wastewater). The concentration of suspended solids remaining in the liquid fraction should be as low as possible, since this can compromise equipment in the latter stages of the filtration processes.
Purification involves the use of a permeable membrane which retains contaminants while allowing water to pass through. Specific membranes filter specific contaminants at a molecular level. Reverse osmosis membranes will retain small molecules and ions while ultra filtration membranes retain soluble macromolecules and larger particles. This separates the digestate wastewater into a permeate stream potentially suitable for direct discharge and a concentrate, potentially suitable for us as a fertiliser.
This step reduces the the loading of biological oxygen demand (BOD) and ammonia in the digestate by aeration in the presence of bacteria. This is an aerobic activated sludge process with a nitrification and a denitrification step. There are various methods available, for example via membrane bioreactors (MBR), sequencing batch reactors (SBR), moving bed bioreactors (MBBR) and fixed bed biological reactors (FBBR). The most suitable method of treatment will depend on the composition of the digestate wastewater, environmental regulations and site specific requirements.
Although this step most commonly treats the digestate liquor prior to discharge, it is also a suitable treatment for the original digestate (wet composting) or as a pre-treatment stage.
Dissolved Air Floatation
Dissolved air flotation (DAF), is particularly effective for treating digestate with high nitrogen concentration, for example, cattle and pig manure. Dissolved air flotation can remove as much as 80% of the organic load and 65 % of the nitrogen load of wastewater. As a form of pre-treatment, DAF can significantly reduce the solid fraction of digestate, reducing the overall volume by a factor of six.
Chemical Treatment of Digestate Liquid Waste
High concentrations of nitrogen and phosphorus can be removed from digestate wastewater by means of struvite precipitation or crystallisation. The conditions for struvite precipitation usually require pH adjustment and magnesium ion addition. The recovered struvite can then be used as an inorganic fertiliser.
Silage Clamp Leachate Collection and Treatment
Leachate from large scale silage clamps at an anaerobic digestion plant is a highly concentrated waste stream that requires collection and treatment prior to discharge. Factors effecting the constituents of the leachate include the type of feedstock and method of ensilage. Silage effluent ranks among the highest sources of potential pollution and so there are strict environmental regulations in place to prevent this from occurring. The acidity of silage clamp leachate causes corrosion to steel and damage to concrete making it a challenge to process. Therefore the collection, treatment and disposal of silage effluent requires an engineered solution to address these challenges and to meet the unique requirements of the biogas plant. Biocell engineers cost effective and robust solutions for the treatment of silage clamp leachate, contact us for a free design proposal.
Site Specific Liquid Digestate Waste Treatment
The most suitable method of treating liquid digestate wastewater will depend entirely on the composition of the original digestate, the site specific requirements, enivronmental regulations and energy use. To find out more about the cost of a treatment plant for unique digestate wastewaters, don’t hesitate to get in touch.
How to buy a Treatment System for Digestate Liquid Wastewater
Get in touch to speak with a member of our technical sales team about a treatment plant for digestate liquid waste. We can provide you with a free quotation or answer any questions you may have about treating digestate wastewaters. We are happy to give more information or make recommendations on the best solution for your unique treatment requirements. Have a look at some of our commercial case studies to see some of our work. Our products and solutions are independently tested and certified and meet the regulatory local and national standards.