FREQUENTLY ASKED QUESTIONS

The technology to be used runs under controlled temperature, it will need the contribution of energy, which can come from the combustion of methane.
The fermenter has thermal insulation systems, and can even work indoors, furthermore the technology of water purification through SBR is a classic and very mature technology and it has being used intensively in any European country.
The temperature of anaerobic digestion process is 35°C, in countries colder than the “Madadero del Sur” pilot plant, the power consumption will be greater. In fact, a lot of Wastewater Treatment Plants (WTP) from different European countries foresees the mesophilic sludge treatment. However, we propose to operate at upper Higher Range Temperature (HRT).
Another factors governing algal treatment performance is the light. While the light performance in southern locations is relatively high throughout the year, northern latitudes have much better light performance in the summer time. This is evidenced by the well-known fact that the richest areas of planktonic blooms in oceans are far north. In southern areas high temperatures may give problems because of evaporation and we might be out of the optimal conditions for significant part of the day. In northern latitudes there is a potential problem of freezing.
So we might expect that algal bacterial treatment in northern latitudes will outperform the same technology done in south for approximately half of the year. For the rest of the year it might be required to revert to a classical processing.
In order to solve this problem the W2R consortium is thinking about a hybrid configuration - the SBR in is surely an essential part this configuration - it could work under different conditions in function of the season.
Algal species selection is a crucial point to fine tune the plant in a given geographical area, real scale testing will have to be performed for a pilot installation in colder latitudes, in any case these activities are also expected for each new plant.
Most of the processes that are combined in the W2R flow-sheet are developed in closed-vessels, except algae treatment. This fact makes the proposed flow-sheet climate-independent. Of course, biological processes are temperature-dependant but in case of extreme low temperatures heat can be applied to reach the optimum operating conditions.

For algal treatment salt content is absolutely no problem. There are many algal species that are halophilic, even extremely halophilic. Part of the technology that is sensitive to higher salt concentrations is anaerobic digestion. Even for this part the solutions are being developed, for example within the Saltgae project which shares some of the consortium members. Within the Saltgae project treatment of the saline waters with salt levels around 100 g/L are being demonstrated. A combination of technologies from both projects may be required in special cases of high salinity in the incoming wastewater.
In the frame of W2R project, a sampling campaign has been carried out in a slaughterhouse in order to check the raw wastewater composition and prepare the design of the pilot plant. Conductivity has ranged between 1484 and 4163 (µS/cm) (2724 µS/cm, mean value). Those values are high in comparison to the ones in urban wastewaters but many not supposed any problem to the biological.

Mesophilic temperatures are not able to reduce to zero any pathogens bacterial at all content in the sludge.
Changing the pH in the ponds may make Salmonella not surviving, but this condition should be still checked further more detailed studies.
In any case by using thermic and chemical energy coming from the anaerobic digestion, it would be possible to hygienise the substrate.
Concerning the treated water from the water line (SBR + membrane module for nitrates’ recovery) it would meet the standards for water reuse in many purposes although zero pathogens content is rarely guaranteed.

According to previous projects in treating the biogas liquid phase digestate, pathogens do not survive under aerobic conditions in algal ponds. The research should be fine-tuned. Cat 2 materials have never been used in the demo plant and it might be interesting to focus on prions biological resilience after treatment. It might be possible to test the behaviour of algal-bacterial approach for Cat 2 and Cat 1 animal by-products.
A thermal treatment would certainly reduce any risk to almost zero.
W2R project implements the circular economy approach on the wastewater generated in the slaughterhouse and meat sector but does not deal with the animal-by products (category 1, 2 or 3).

Legal limits for release of the treated wastewater to the environment are different in different countries. If there is a way to treat the wastewater by conventional methods there is also our way to do it through the W2R design using a more cost effective and environmental friendly protocol.
The most relevant part of the W2R design is an SBR which ordinarily is the only part of the conventional system. The nutrient recovery part will only lower the impact to the environment compared to conventional treatments. If it can be done in a conventional way, we can only do it better.
W2R approach aims to recover the organic matter and nutrients from the wastewater of slaughterhouse and meat industry. The combination of an SBR (aerobic technology) and membrane module (including RO) ensures a high quality effluent even potentially reusable in different purposes.

We have been using standardized microbiological plate methods to test pathogens. There may be other more specific tests, nevertheless the W2R technology benchmarked with the conventional one is for sure more efficient.
The monitoring parameters that will be employed to check the performance of the W2R pilot plant will be determined through standardized methods (approved by ISO and other relevant institutions).