Biogas Plants Biodigesters

The bio-digesters are «biological engines» allowing the transformation of organic matter (liquid or dry) into biogas and stabilised organic fertiliser.


Biogas plants are facilities with three purposes:

  1. Treat the organic matter (liquid or solid) by biological process.
  2. Generate a renewable natural gas for energy usage.
  3. Stabilize the organic material for better use as fertilizer.

Bio-digesters convert organic matter carbon in methane (CH4) and carbon dioxide (CO2). The nutrients in organic matter (N, P, K) are not removed and are the by-products (sludge, treated effluent).



Main models developed by BIOTEC:

  • UASB = Upflow Anaerobic Sludge Blanket (see more)
  • RAC ® = Contact Anaerobic Reactor (see more)
  • RAFAC ® = Contact Upward Flow Anaerobic Reactor (see more)
  • DAR ® = Dry Anaerobic Reactor(see more)

Composting plants

Composting is a technique of processing organic by-products (solid).

The objectives of the composting process are:
  • Reduce the volume and the weight of material to be transported
  • Stabilize organic matter to turn it into compost
  • Replace chemical fertiliser in the field
  • Control odours
  • Recycle the nutrients to the soil
  • Evaporate wastewater and sludge

Depending on raw material, land available, environment, weather conditions, objectives and industry policy, BIOTEC engineers composting plants by front turner (traditional system), by side turner and/or by forced aeration.


  1. FT: Traditional system with front turning
  3. LT: Alternate system with side turning which allows greater height of piles and avoid spaces between piles
  5. FV: Forced aeration. In this system it is not necessary to proceed to turning as long as the material is sufficiently loose

Liquid Organic fertilisation systems

For the effluents and wastes not to be discharged in rivers or landfills, it is necessary to find ways to return the organic matter and nutrients they contain to the soil. Agronomy and agricultural engineering are a complement to environmental and sanitary engineering. Fertilisation with fresh or decomposed organic material is already common practice in agriculture around the world. Liquid Organic Fertilisation is less well known but equally important.

When liquid application technologies do not exist or are not satisfactory for technical or financial reasons, BIOTEC engineers innovative solutions for organic fertiliser application. The principles and features largely depends on the type of crop. This is the case of "FORLIM"® (Liquid Organic Fertilisation Monitored System), that allows the application of treated effluent and sludge from the bio-digesters in a controlled fashion on the plantations. The FORLIM uses a computer system (SCADA) and a GIS (Geographical Information System) allowing online control and tracking of the fertilisation process.

The FORLIM generate periodic reports on fertilisation for the management and/or environmental authorities.

Dosage of nutrients per hectare per year are similar to the dosage used for chemical fertilisation.

  • Zero discharge to rivers and water bodies
  • Providing and adding value to anaerobic sludge and effluents
  • Replacement of chemical fertiliser in the estates
  • Improvement of the soil
  • Increase in performance
Order of magnitude:
Crop Dosage (liquid organic fertilizer).
OIL PALM: 100 - 300 m3/ha-year
SUGARCANE: 50 - 300 m3/ha-year
CITRUS: 1000 - 2000 m3/ha-year


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 or P removal rates that the wastewater treatment plant’s CAPEX and OPEX make the agribusiness no competitive anymore.

With its technological partner SSP from India (, a company specialized in evaporation and drying (for food, aromas and effluents), BIOTEC developed the concept of effluents BIODRYING.

The principle is the following:

  • Stage 1: methanisation of the effluents to generate fuel gas and to concentrate it in nutrients (by a factor of 4, on average). Consequently, an effluent with 3% K2O, for example, ends up having 12%.
  • Stage 2: 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 MSE (Multi-Stage Evaporators) with low energy consumption.
  • Stage 3: Drying the "digestate”, until producing a very fine powder with only 5% humidity. The dryers are "SPRAY DRYERS" and use the same biogas as fuel.

The final product is a bio-fertilizer powder, with 40 to 50% stabilized (digested) organic matter and 30 to 40% macronutrients (nearly similar to a chemical fertilizers).

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 marketed as granules.

Consequently, the "bio-drying" allows:
  • Avoiding any discharge other than crystallized 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-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 6 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 solve a major environmental problem.



BIOTEC designs, builds, implement and supervises its solutions on an industrial scale.


The implementation of these projects can be done in two ways:
  1. Full/partial turnkey : BIOTEC is responsible for the entire project, from the design and construction of the plant to commissioning. For partial turnkey, the client is responsible for civil works and the direct purchase of certain equipment.
  2. Integral Engineering: Includes: design, supervision of works, inoculation, start-up. Advice on purchases and / or project management is optional.


A good installation must be correctly operated to take advantage of its full potential. BIOTEC is committed to its customers and will operate the plant up to two years. In this way the plant will operate at the designed performance (KPI) and the customer’s operational team can be fully trained.

BIOTEC operates plants under two models:
  1. Management: BIOTEC participates in the operation with its own staff, leading and training the client’s team.
  2. Supervision: On-line monitoring (SCADA system) with periodical audits.


BIOTEC designs and builds thinking
as operator