Description

The  innovation of the reactor lies  on  the synergy between two of the most efficient processes for  the removal of pesticides from Agro-wastewater, namely nanofiltration and photocatalysis. This  synergy concludes to significant process intensification that in turn leads to the reduction of the reactor dimensions (CAPEX) and the concomitant cut in the operational cost (OPEX). The  consortium strives also to ensure the autonomous operation of the process and safeguard stable efficiency that will not depend on  the seasonal conditions (solar irradiation) and the agro-wastewater composition. In addition, the feasibility of achieving 60 % reduction in the required transmembrane pressure, significant extension of the life  time of the process (2-fold) and higher effectiveness in the elimination of organic and inorganic pollutants (+99.5%) by  developing the next generation aligned SWCNTs based photocatalytic monoliths, will be verified with the purpose of integrating them with the PNFR process.

Consequently, the LIFE PureAgroH2O project proposal is unique and demonstrates evidence of innovation due to the implementation of state-of-the-art technologies in water treatment (photocatalytic nanofiltration), advanced materials (novel VLA-TiO2 augmented aligned SWCNT membranes), lighting (remote irradiation with optic fibers and new light emitting diode products) and powering (photovoltaics, energy storage technologies) and integration of the aforementioned sub- technologies into a final commercially available PNFR reactor. The  full-scale prototype system is capable of automatic control and recording and can be exploited in many commercial applications. 

It could be used for treating:

1. End-of-the-pipe wastewater effluents generated in fruit-industry
2. Wastewater produced during the washing of the spraying machinery, phytosanitary treatments equipment and containers of agricultural chemicals
3. Greywater of hotels, public building and houses
4. Effluent of biological treatment plants to eliminate substances of low  biodegradability
5. Drinking water, to confront the problem of taste and odor that can arise from a variety of compounds
6. Effluent of anaerobic fermentation in biogas production and recycle the water

At the moment a lab  scale PNFR reactor has been designed, constructed and patented and different types of photocatalytic monoliths and stabilized VLA-photocatalysts have been tested for  their efficiency to purify water from organic and inorganic pollutants. These studies led to numerous publications in high impact factor journals, elaborating significant issues regarding the synergy between nanofiltration and photocatalysis and the energy efficiency of the process.
However, to achieve an almost 10 fold  increase on  the water production capacity (from 1.5 m ³ /day to 15 m³ /day) of the already existing reactor, the selection of an appropriate membrane/photocatalyst configuration and irradiation system is of utmost importance. This  requires limited research effort on system design modifications and subsequently testing, in order to ensure a large amount of activated photocatalyst per unit volume of treated fluid, without any loss of the water processing capacity.

The  majority of photocatalytic reactors suffer from low  light utilization and mass transport limitations and for  this reason they are still  limited to the laboratory-scale. Contrary, the prototype of the proposed hybrid NF/photocatalysis idea, as described in the European patent EP 2 409 954 A1, is already tested as a “proof of concept” of the feasibility for  upscaling the process. In this context, honeycomb monolithic membranes will be used as unique SWCNTs and photocatalyst supports, that contain a large number of small channels in parallel, through which the reacting fluid  flows and the catalyst is deposited on  the walls of the monolithic channels. In order to examine this possibility, a novel way of irradiation via  optic fiber bundles will be implemented in a way to receive light alternatively from artificial sources (LED powered) and from the sun via  a system of collectors, coupled collimators, reflecting mirrors and condenser lens.

Furthermore NCSRD  has already developed novel Vis-light active photocatalysts which are based on modified (anion doped) TiO2  and reduced graphene oxide (rGO)/TiO2 composites. The  successful deposition of these materials on  the shell and lumen surface of the honeycomb aligned SWCNTs monolithic membranes as well  as, their embedment into aerogel type light transparent polymeric fibers is expected to have a tremendous impact on  the energy demand for  irradiation of the active surfaces. The  target is to abstract as low  as possible energy from the batteries of the PV system by  fully exploiting solar irradiation.
The  implementation of PNFR (photocatalytic nanofiltration) process in Agro-wastewater treatment is unique and it has not been presently available in the agricultural industry.
Currently, NF has the capacity to reject agricultural chemicals with a retention efficiency of 35-98% depending on  the molecular size and charge of the substance. Integration of Nanofiltration (NF) with low  pressure reverse osmosis (RO)  has already been industrially tested in pesticide removal for drinking water supply (Paris, France NF plant [a]  (140,000 m³/day) and Saffron Walden, England NF plant [b]  (3,000 m³ /day)). NF-RO integration ensures 100% rejection efficiency, though with much higher energy consumption.

Examples of relevant technologies are also available under the framework of LIFE projects.

LIFE Aquemfree (LIFE13  ENV/ES/000488) uses the 1st generation photocatalysis/membrane process.

LIFE WATOP (LIFE11  ENV/ES/000503) makes use of nano-adsorbents embedded into membranes for removing Pharmaceutical Products included within the tertiary treatment of wastewater treatment plants.

LIFE WOGAnMBR  (LIFE13  ENV/ES/000779) demonstrates the use of membranes in anaerobic digestion for  the production of methane rich biogas while achieving superior effluent quality suitable for  post- treatment and reuse applications.

PURIFAST (LIFE07  ENV/IT/000439) demonstrates a hybrid wastewater treatment system, which is based on  Ultra Filtration (UF) and an innovative Advanced Oxidation Process (AOP),  the sonochemical process.

The  advantages of PNFR as compared to the aforementioned processes emerge due to simultaneous irradiation of the photocatalytic shell and lumen surfaces of the NF monolith during nanofiltration.  The  photocatalytic action in the feed side is further augmented by  the inclusion of porous fiber stabilized VLA-photocatalysts. Thus, contrary to what normally happens in UF, NF and RO processes, the retentate effluent becomes less concentrated in pesticides than the feed. This  is an important attribute as it permits the recycling of retentate back to the feed without affecting the retention performance of NF. In this manner high water recovery up to 95% can be achieved without the need for multiple membrane cascades, the production of heavily concentrated toxic condensates is avoided and membrane fouling is limited since most of the fouling prone substances are photocatalytically degraded upon their attachment on  the membrane surface. Moreover the PNFR addresses the inherent incapability of NF to retain smaller organic molecules since the permeate (filtrate) slips down the lumen photocatalytic surface of the monolith where organic substances are photocatalytically degraded. Confirmed photoinduced hydrophilicity endows membranes with higher water flux  and leads to significant reduction of the energy requirement (transmembrane pressure), carbon footprint and CAPEX of the process. Last but not least, the induced by  the simultaneous NF-photocatalysis action, anti-fouling properties and capacity of the process to operate with complex mixtures of inorganic and organic substances, constitute it as a novel, beyond the-state-of-the-art approach to address the challenge of wastewater remediation and recycling, thus providing a unique tool not only in the fruit industry but also in other areas.

The further development and combination of the existing photocatalytic membrane, irradiation and powering technologies requires research, design, building, testing and evaluation. In this respect, the project emphasises the pilot character of the full-scale PNFR. Despite many systems are available in the market for  wastewater treatment, the PNFR substantially differs from them and it will generate foreground IPR, which will be agreed and shared among the partners.