ELECTROCOAGULATION TECHNOLOGY (EC)
The pilot plant demonstration has been monitored during 12 months (the first tests of the pilot EC were done on April 2018 at half of its capacity and from July 2018 the pilot plant was complete and operative).
- Parameter analysed in continuous mode: Total phosphorus and Total nitrogen
It has been observed that the influent is not homogeneous and depending on others components dissolved in the raw water, the efficiency removal varies:
Figure 1. A) Total phosphorus removal during long-term operation. B)Total nitrogen removal
- pH and temperature: pH and Conductivity were measured during the long-term operation of the EC units. The results of both parameters analyzed in the influent and effluent after treatment in the EC system are shown in Fig. 11.
Figure 2. A) Variation of pH during EC long-term operation. B)Temperature increases slightly in continuous-mode.
FLUIDISED BIOELECTROCHEMICAL BED REACTOR TECHNOLIGY (FBBR)
Comparative study at pre-pilot sce: FBBR technology vs Conventional AD
The continuous operation of a pre-pilot FBBR was performed in order to study the robustness of the proposed technology. In addition a pre-pilot conventional anaerobic digester (AD) was operated to compare the behaviors and the efficiency of both systems. The final objective of the operation of these reactors is to recover relevant information for the operation of the pilot FBBR.
Both pre-pilot reactors were inoculated at the same time and the operational parameters were the same in order to obtain a high repeatability of results.
The operation of the pre-pilot FBBR and AD was also mandatory in order to obtain information about the biogas production and composition due to the experimental problems to obtain information of this key parameter at lab-scale. In addition, in order to increase the knowledge about this innovative technology the behavior of the FBBR technology should be compared with the conventional AD for the validation of the technology. This comparing studio has been performed facing different scenarios with both technologies.
Test 1: Operation of FBBR and AD technology at high COD inputs
Test 2: Operation of FBBR and AD technology with pollutants in the influent
Test 3: Operation of FBBR and AD after a starving period
Test 4: Operation of FBBR and AD at low temperature (25ºC)
Results of the different scenarios and the biogas generation are described in the next figure
Fig.3. One year operation of a AD and FBBR reactors under different operational conditions.
The one-year operation indicates the robustness of the tested technology (FBBR) which is strictly necessary for the further development and commercialization of the technology
Finally, among unbalances, pre-pilot reactors were continuously operated until total recovery of the efficiency of the technologies were achieved. During the operation of the reactors with steady state values, biogas was monitored in order to obtain more information about the energetic value of this gas flow. Obtained result can be seen in Fig. 4.
Fig. 4 Biogas energy content. Energy valorization of the produced biogas
Fig.4 shows the higher energy content in the FBBR biogas due to the continuously production of hydrogen, which is properly mixed with the methane yield increasing the energy power that could be recovered comparing with the obtained value in conventional technologies were the bioelectrochemical production of hydrogen does not take place
Pilot plant parametrization and demonstration
With the precious obtained information of the lab-scale FBBR and taking into account the competitiveness of the bioelectrochemical reactor in front of conventional AD (experiments at pre-pilot scale), the pilot FBBR was optimized in order to enhance the efficiency of the technology. The wastewater treatment capacity is 1 m3/h during the long-term operation.
- pH and conductivity: pH and Conductivity were measured during the experimental analysis of the FBBR reactor. The results of both parameters analyzed in the wastewater and after the bioelectrochemical system are shown in Fig 5.
Fig. 5. pH and conductivity of the wastewater and treated water during the continuous operation of the pilot FBBR
It was observed that the pH of the treated water was almost the same than the obtained for the wastewater that could be a great advantage of the technology because the pH of the treated water is under the legal limit for water discharges.
- COD removal: The COD concentration in the wastewater and the treated water was monitored during the experimental analysis in order to know the wastewater treatment capacity of the bioelectrochemical reactor and the COD removal performance. The obtained results are found in Fig 6.
Fig. 6. COD concentration and COD removal during the continuos operation of the pilot FBBR
During the experimental period it was observed a high performance of the FBBR from the COD consumption point of view, achieving values around the 82% – 85% of COD removal. This high COD consumption removal is associated to the anode polarization (1 V) which accelerate the COD consumption rate due to the action of electroactive bacteria. No re-inoculation was needed during the FBBR operation that gives an idea about the robustness of the technology.
- Nutrients removal: Nutrients removal were also monitored in order to check the capability of the FBBR reactor in the removal of nitrogen and phosphorous (Fig. 20). It is important to notice that total nitrogen and total phosphorous were analyzed and shown in the figure.
Fig.7. Nutrients removal during the continuous operation of the pilot FBBR
Attending to the results, total nitrogen and total phosphorous was removed up to 50% in both cases during the experimental period. Nevertheless, big deviations were found so further analysis should be done in order to optimize the determination method. The decrease of those nutrients are a competitive advantage respecting the conventional anaerobic digestion and an advantage from the environmental point of view.
Finally, energy consumption and generation has been monitored to give relevant information about the development of the technology and the technical and economic viability of the bioelectrochemical unit. The energy consumption was calculated attending to the potentiostat consumption, while the energy generation was obtained taking into account the electric power generation by electroactive bacteria and the energetic potential of the enriched biogas (methane + bioelectrochemical hydrogen). Those results can be observed in Fig.8.
Fig.8. Energy consumption and energy generation during the continuous operation of the pilot FBBR
In Fig.8 can be shown how the produced enriched biogas has a high energy content that could be valorized, while the energy consumption related with the potentionsat (necessary for the anode polarization) is very low comparing with the energy generation.
ULTRAFILTRATION AND DISINFECTION UNIT
After the installation of both systems, the continuous operation of both technologies has been developed. The UF unit has been fed with the electrocoagulation and the FBBR effluents in order to achieve the final treated water flow (10 m3/h). The final treated water achieve with the Spanish Law (R.D 1620/2007)
In the next figure (Fig.9), the results obtained in the UF (and the disinfection unit) are shown
Fig.9. UF+UV results. Treated water generation
As can be seen, after the UF unit, the turbidity is partially removed, as the total suspended solids. As previously said, the treated water accomplish with the Spanish Law, which possibly impact in the environment and allows to accomplish with the final goals of ANSWER project.
The ANSWER solution has demonstrated to be suitable for the wastewater treatment from the technical point of view as shown during this report. The combination of electrochemical technologies (electrocoagulation and fluidised bioelectrochemical reactor) produces a very high-quality effluent. The tertiary treatment post-treatment of the final effluent (UF and UV disinfection) improves the quality of the final effluent that accomplish with the national law R.D 1420/2007 for water reuse.
Fig.10. Nutrients removal with ANSWER technology: influent and effluent after UF+UV treatment