1. WASTEWATER TREATMENT

In order to reduce investment costs, and above all to cut operating costs, BIOTEC uses UASB (Upflow Anaerobic Sludge Blanket) anaerobic reactors as the "basic unit" of its plants. It is a design developed towards the end of the 70s in Wageningen (Holland) by Professor Lettinga. This basic unit has a decontamination efficiency rate that ranges from 65 to 90% depending on the type of wastewater concerned (its concentration and its biodegradability). It generates very little biological sludge (a fifth of that generated by conventional aerobic plants) and this sludge is "stabilized" and easy to dehydrate. It also generates biogas as a by-product of fermentation.

When increased efficiency or odour-free effluent is required, BIOTEC adds an aerobic post-treatment system to the UASB reactor such as trickling filters or stabilizing ponds in rural areas. These are the only two aerobic technologies that do not rely on electro-mechanical equipment for oxygenation. We also use submerged aerobic filter systems, SBR or physical-chemical systems.

Depending on environmental requirements, BIOTEC also equips its basic units with additional units for the removal of pathogens, sulphurs or nutrients and wherever possible always tries to use the ground as a post-treatment unit and to convert the wastewater into a consumable for development taking advantage of the by-products from treatment plants.

In addition to the UASB or "anaerobic filter" type reactors, BIOTEC also uses covered anaerobic ponds for the treatment of high-loaded agro-industrial effluent. Covering the ponds with plastic membranes (liners) prevents the release of methane into the atmosphere (greenhouse effect) and allows it to be used to produce electricity and/or thermal energy.

Applications: Sewage (municipalities, housing developments), cattle, pig and chicken slaughterhouses, palm oil mills, oil refineries, paper mills, yeast plants and the coffee, dairy, meat, sugar, sweet and animal feed industries in general, breweries, fizzy drinks manufacturers, wine-producers, distilleries, cattle raising, pig rearing, etc.

Using the same BIOTEC conception that enhances the value of organic matter and nutrients as agricultural fertilizer, BIOTEC builds composting systems in windrows or silos associated with marketable systems and the application of the compost produced.

The compost aeration system is by manual or mechanical turning or forced draught.

With respect to garbage, BIOTEC also provides composting systems prior to selection. This reduces selection costs and therefore these are generally better suited to poor countries with low organizational or administrative capacity, especially on the small and medium scale. In these cases, selection is done with screens after composting and is much easier.

Applications: urban waste, sugar mill filter cake, sludge and solids from wastewater treatment plants, fruit husks, coffee residue, waste from flower-growing, etc.

Odours are usually made up of volatile organic compounds, sulphur compounds (sulphurs, mercaptans) and/or nitrogen compounds (ammonia, amines).

All these compounds can be treated chemically or biologically.

To reduce operating costs and to prevent the discharge of chemical effluent, BIOTEC recommends the use of biological odour removal by means of the following systems:

• Biotrickling filters ("Biotrickling Filters")
• Compost filters ("Biofilters")

Applications: Wastewater treatment plants, slaughterhouses, rendering plants, chemical industry, etc.

BIOTEC has developed biological systems for removing H2S from biogas and implements small and large size biogas use projects for:

- Cookers (industrial cookers and urban network)
- Gas lighting
- Heating (water heaters and industrial steam boilers)
- Direct generation of electricity using gas turbines, gas engines or dual-fuel engines (diesel engines adapted for biogas and fuel co-burning)