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:

  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 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).

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

Composting Plants

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

The objectives of the composting process are:
  • 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.


  1. FT: Traditional system with front turning.
  2. LT: Alternate system with side turning which allows greater height of piles, reducing foodprint. Does not require roof.
  3. 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.

  • 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 (, 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:

Stage 1: 

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.

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 MEE (Multi-Effect 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” 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.



BIOTEC designs, builds, implements, supervises, inoculate and commission its solutions on an industrial scale. 

Two modalities:

1. Full/partial turnkey:

BIOTEC is responsible for the entire project, from the design and construction of the plant to the commissioning.

As an option, the client can assume civil works and/or buy some equipment directly.

2. Integral Engineering (EPC-EPCM):

Includes: design, supervision of works, inoculation, start-up (commissioning). 

Can also include, as an option, a support for purchases and/or project management.


BIOTEC usually operates its plants for up to two years, or supports its clients in the routine operation all the time required. By this way, BIOTEC commits with the KPI for a long period and the client benefits from its experience and from technology upgrading year after year.

It is definitively more comfortable for (biogas, composting, fertigation or bio-drying) plants operators to have a permanent support from the designer (on-site or remote).

Two modalities:

  • Management:

BIOTEC participates in the operation with its own staff, leading and training the client’s team.

  • Supervision:

On-line monitoring (SCADA system) with periodical audits.

BIOTEC designs and builds with the operation in mind.


1. Conceptual engineering / Feasibility studies / Audits:

When a client is not defined in advance about the project to implement to treat and valorize effluents and waste, BIOTEC advises to hire a preliminary phase of “Conceptual engineering” to evaluate options, with their advantages, disadvantages and approximate costs, looking for the most appropriate to its specific case. This phase requires a wide experience of all available technologies and their costs. BIOTEC set-up two CONSULTANCY COMPANIES to do that specialized job.

See the window « CONSULTANCY » on this WEB site and the brochures and WEB sites of EVE (Effluents Valorization Engineering) and POME.

See Brochures “EVE”                                           See Brochures “POME”

2. CDM projects (Clean Development Mechanisms):

BIOTEC has been world leader on CDM projects for methane capture in the agro-industry between 2006 and 2012, during the Kyoto Protocol period, and in particular in the palm oil industry to reduce its Greenhouse Gases emissions.

Eight BIOTEC biogas projects have been registered by UNFCCC (United Nations) as CDM during that period, with an average methane capture of 40.000 tons CO2 per project per year.

The Eecopalsa project in Honduras (# 492 of the CDM list), commissioned by BIOTEC in August 2006, has been the first one for the palm oil industry. It has been operated by BIOTEC for five years, what means during all the KYOTO period. BIOTEC has therefore overseen the five annual audits, reaching every year the maximum number of CERs (Certificates) allowed by the PDD (Project Design Document).

See Document “CDM references”