Non-conventional EXTensive secondary treatment

HRAP

High Rate Algae Ponds (HRAP) are designed as a secondary treatment for wastewater treatment. This low-cost technology is based on microalgae-bacteria consortia in which the first microorganism produces oxygen which bacteria uses to degrade organic matter in the wastewater. The symbiosis of such microorganisms makes it possible to depurate wastewater with low energy demand. 

High Rate Algae Ponds have not yet been used in full-scale installations in Europe. Aqualia has installed and operated various pilot and demo HRAP treating WW in Spain, and CENTA has also installed a pilot 500 m2 HRAP at their facilities. 

The aerated HRAP in INTEXT is designed for 250 population equivalent (PE) treating a WW flow of 50 m3/day, will consist of 2 ponds in parallel with a total surface of 500 m2. A state of the art non-aerated 250 m2 HRAP with dissolved air flotation harvesting will be constructed to be compared to an INTEXT aerated HRAP with clarification by gravity.

a) HRAP; b) Floating wetlands

Constructed aerated wetlands

‘French’ constructed wetlands (CW) treating raw domestic WW have reached international recognition over the last few years. These systems are based on the integration of urban wastewater to natural sand filters in which plants grow. Interaction of plant species with microorganisms and the effect of the biofilter make it possible to reach high depuration performance with good landscape integration and low environmental and energetic impact. 

SYNTEA has developed an intensified version of this CW called Rhizosph’Air® that allows to reach enhanced effluent quality with lower footprint than CW with passive aeration. Furthermore, the development of smart monitoring and operation control could offer a very high added value to CW but still need a validation at demo scale to make it marketable.

a) Constructed aerated wetlands; b) Rhizosph’Air®

Floating wetlands

Floating wetlands consist on a water matrix in which emergent plants grow along the surface. The upper parts of the plants grow above the water level while the roots extend down in the water matrix playing a crucial role on nutrient and organic matter uptake. Roots provide surface and nutrients for the growth of bacterial biofilms which develop biochemical process such as nitrification/denitrification. This natural system performs wastewater treatment by the addition of wastewater to the liquid matrix.

These systems can be an alternative or a better option to CW, as they need less surface and can avoid the problem of clogging. PROJAR, has already adjusted the floating capacity and found the best-adapted vegetation. Now it is necessary to be tested in a greater scale to validate the constants of the model employed for its design. 

The newest advance will be the implementation of a solar driven aeration system to increase the oxygen content in the water column and improve the hydraulics, thus enhancing its general performance.