Biogas Plants (Biodigesters)
The bio-digesters are «biological engines» allowing the transformation of (liquid or dry) organic matter into biogas and stabilised organic fertiliser.
Biogas plants are facilities with three purposes:
- Treat the organic matter (liquid or solid) by biological process.
- Generate a renewable natural gas for energy usage.
- Stabilize the organic material for its better use as fertilizer.
Biodigesters convert organic matter (carbon), into methane (CH4) and carbon dioxide (CO2). The macro and micro nutrients are not removed by the anaerobic digestion. Both treated effluent as well as sludge can be valorized as liquid or solid biofertilizers as part of the BIOTEC concept of Zero Discharge Milling (ZDM).
The BIOTEC added value:
- In the biogas business since 1984
- Three specificities:
- Operator (à designs and builds keeping operation in mind)
- Focused on tropical countries
- Digestate valorization
Main biodigesters models developed by BIOTEC:
- UASB = Upflow Anaerobic Sludge Blanket
- RAC ® = Contact Anaerobic Reactor
- RAFAC ® = Contact up Flow Anaerobic Reactor
- RAS ® = Dry Anaerobic Reactor (Visit agrogaz.com)
Composting is a technique for processing (solid) organic by-products.
- To Reduce the volume and the weight of material to be transported.
- To stabilize organic matter to turn it into compost.
- To replace chemical fertiliser in the field.
- To control odours.
- To recycle the nutrients to the soil.
- To evaporate (biologically) water from wastewater and sludge.
Depending on raw material, land available, environment, weather conditions, objectives and industry policy, BIOTEC designs composting plants aerated by front turner (traditional system), by side turner and/or by forced aeration.
- FT: Traditional system with front turning.
- LT: Alternate system with side turning which allows greater height of piles, reducing foodprint. Does not require roof.
- FV: Forced aeration: Very compact. Only for specific cases.
Liquid Organic Fertilization Systems
Liquid fertilization with raw or treated effluent is one of the ways to achieve the concept of “Zero discharge” to the environment. Agronomical and agricultural engineering are a complement to environmental and sanitary engineering. Solid Fertilization with fresh or degraded waste is already a common practice in agriculture all around the world. Liquid Organic Fertilisation is less known but equally important.
Typical spray or drip liquid application technologies can often be used, as well as spraying trucks. In some special cases, like citrus and oil palm, BIOTEC had to engineer innovative solutions for effluent application. This is the case of “FORLIM”® (Monitored Liquid Organic Fertilization) that allows the dosed application of treated effluents and of sludge on plantations. The FORLIM includes a SCADA and GIS (Geographical Information System), allowing an online monitoring of the fertilization.
The FORLIM technology generates periodic reports on fertilization for the management and/or environmental authorities.
Dosage of nutrients per hectare per year are similar to the dosage used for chemical fertilization.
LIQUID ORGANIC FERTILIZATION can achieve:
- Zero discharge to rivers and water bodies.
- Effluent and sludge disposal and valorization.
- Chemical fertilizers savings (replacement).
- Soil Improvement.
- Yield Increase.
- Better resistance to parasitism (illnesses).
In many cases, the Environmental Authorities do not allow any discharge to the river (it happens frequently with cane vinasses) or ask so high COD, BOD, N, P, or color removal rates that the wastewater treatment plant’s CAPEX and OPEX make the agribusiness not competitive anymore.
With its technological partner SSP from India (sspindia.com), a company specialized in evaporation and drying (for food, aromas and effluents), BIOTEC developed the concept of ZERO DISCHARGE MILLING thanks to effluents BIO-EVAPO-DRYING.
BIOTEC/SSP developed three technologies:
1. Co-composting of concentrated effluents with solid biomass.
Example: Vinasses with sugarcane mud / POME with EFB in the palm oil industry.
2. Raw effluent evaporation (in Multi-Effects Evaporators-MEE) + Drying
Example: Transformation of POME into Animal feed (powder). Very convenient if exhaust steam is available after steam turbines.
3. Bio-evapo-drying The principle is the following:
Methanization of the effluents to generate fuel gas and to concentrate it them in nutrients (by a factor 3 to 4, on average). Consequently, an effluent with 3% K2O (on dry matter-TS), for example, ends up having 12% K2O.
Evaporation of the methanized effluent, using the biogas as fuel. The evaporator delivers a “digestate” concentrated in nutrients, which 25 to 40% dry matter (DM) depending on the case. The evaporators are MEE (Multi-Effect Evaporators) with low energy consumption.
Drying the “digestate”, until producing a very fine powder with only 5% humidity. The dryers are “SPRAY DRYERS” or “PADDLE DRYERS” (the latest one when mixing MEE concentrate with sludge cake). Dryers and also use biogas as fuel.
The final product is a bio-fertilizer powder, with 40 to 50% stabilized (digested) organic matter, rich in fulvic acids, and 30 to 35% macronutrients (nearly like a similar to a chemical fertilizer).
We have the possibility of separating the final product into a soluble fertilizer, which is usually sold as powder, and an insoluble one, which is usually used locally or can be marketed as powder or as granules.
Consequently, the "bio-drying" allows:
- Avoiding any discharge other than transparent condensed water.
- Achieving energy self-sufficiency of the evapo-drying process, at least for high COD effluents, such as vinasses and palm effluents.
- Producing a high added value marketable bio-fertilizer.
The ideal application cases for BIO-EVAPO-DRYING are the distilleries vinasses (spent wash) and palm oil mill effluents, due to their high COD and the strict normativity in some countries like India and Malaysia. SSP has the world leadership in evaporation and drying of methanized effluents and has already equipped 14 distilleries in India in the last 8 years.
SSP is also a leader in the evapo-drying of complex, dangerous or delicate effluents such as pharmacy effluents or landfill leachate. In these cases of effluents with low organic load, we usually choose to evaporate and dry the crude effluent, without prior methanization, as the production of biogas would anyway not be sufficient to fuel the equipment and as the objective is not to produce a biofertilizer but only to solve a major environmental problem.