Daniele Cecconet

Effects of process operating conditions on the autotrophic denitrification of nitrate-contaminated groundwater using bioelectrochemical systems

Nitrates have been detected in groundwater worldwide, and their presence can lead to serious groundwater use limitations, especially because of potential health problems. Amongst different options for their removal, bioelectrochemical systems (BESs) have achieved promising results; in particular, attention has raised on BES-driven autotrophic denitrification processes. In this work, the performance of a microbial electrolysis cell (MEC) for groundwater autotrophic denitrification, is assessed in different conditions of nitrate load, hydraulic retention time (HRT) and process configuration. The system obtained almost complete nitrate removal under all conditions, while nitrite accumulation was recorded at nitrate loads higher than 100mgNO3-L-1. The MEC system achieved, in different tests, a maximum nitrate removal rate of 62.15±3.04gNO3--Nm-3d-1, while the highest TN removal rate observed was 35.37±1.18gTNm-3d-1. Characteristic of this process is a particularly low (in comparison with other reported works) energy consumption: 3.17·10-3±2.26·10-3kWh/gNO3-N removed and 7.52·10-2±3.58·10-2kWhm-3 treated. The anolyte configuration in closed loop allowed the process to use less clean water, while guaranteeing identical performances as in other conventional configurations.

Industrial wastewater treatment with a bioelectrochemical process: assessment of depuration efficiency and energy production

Development of renewable energy sources, efficient industrial processes, energy/chemicals recovery from wastes are research issues that are quite contemporary. Bioelectrochemical processes represent an eco-innovative technology for energy and resources recovery from both domestic and industrial wastewaters. The current study was conducted to: (i) assess bioelectrochemical treatability of industrial (dairy) wastewater by microbial fuel cells (MFCs); (ii) determine the effects of the applied organic loading rate (OLR) on MFC performance; (iii) identify factors responsible for reactor energy recovery losses (i.e. overpotentials). For this purpose, an MFC was built and continuously operated for 72 days, during which the anodic chamber was fed with dairy wastewater and the cathodic chamber with an aerated mineral solution. The study demonstrated that industrial effluents from agrifood facilities can be treated by bioelectrochemical systems (BESs) with >85% (average) organic matter removal, recovering power at an observed maximum density of 27 W m-3. Outcomes were better than in previous (shorter) analogous experiences, and demonstrate that this type of process could be successfully used for dairy wastewater with several advantages.

Evaluation of energy consumption of treating nitrate-contaminated groundwater by bioelectrochemical systems

Nitrate contamination of groundwater is a mounting concern for drinking water production due to its healthy and ecological effects. Bioelectrochemical systems (BES) are a promising method for energy efficient nitrate removal, but its energy consumption has not been well understood. Herein, we conducted a preliminary analysis of energy consumption based on both literature information and multiple assumptions. Four scenarios were created for the purpose of analysis based on two treatment approaches, microbial fuel cells (MFCs) and controlled biocathodic denitrification (CBD), under either in situ or ex situ deployment. The results show a specific energy consumption based on the mass of NO3--N removed (SECN) of 0.341 and 1.602u202fkWhu202fkg NO3--N-1 obtained from in situ and ex situ treatments with MFCs, respectively; the main contributor was the extraction of the anolyte (100%) in the former and pumping the groundwater (74.8%) for the latter. In the case of CBD treatment, the energy consumption by power supply outcompeted all the other energy items (over 85% in all cases), and a total SECN of 19.028 and 10.003u202fkWhu202fkg NO3--N-1 were obtained for in situ and ex situ treatments, respectively. The increase in the water table depth (from 10 to 30u202fm) and the decrease of the nitrate concentration (from 25 to 15u202fmg NO3--N) would lead to a rise in energy consumption in the ex situ treatment. Although some data might be premature due to the lack of sufficient information in available literature, the results could provide an initial picture of energy consumption by BES-based groundwater treatment and encourage further thinking and analysis of energy consumption (and production).

Wastewater treatment with a new electrically enhanced biomass concentrator reactor: trial application and technological perspectives

ABSTRACT Biomass concentrator reactors (BCRs) are an alternative wastewater treatment technology developed as a possible solution to membrane bioreactors’ (MBRs) high construction and energetic costs. BCRs are an alternative based on the same principle of biomass retention, using a coarser filter medium instead of a membrane. A BCR-derived technology enhanced by an electric field called electrically enhanced biomass concentrator reactor (E2BCR) was developed, designed, and tested for wastewater treatment at different organic loads for a period of 100 days. The electrically enhanced reactor showed better chemical oxygen demand (COD) removal performances that the non-enhanced control reactor (90% and 84%, respectively), and a lower fouling tendency. The E2BCR proved to be more energy efficient in comparison with the control reactor in terms of energy consumption per mass of COD removed.

Controlled sequential biocathodic denitrification for contaminated groundwater bioremediation

Nitrate groundwater contamination is a worldwide concern. In this study, a novel 2-stage, sequential biocathodic denitrification system was tested to perform autotrophic denitrification of synthetic groundwater. The system was operated at different nitrate loading rates (66-301u202fgNO3--Nu202fm-3NCCu202fd-1) at constant NO3--N concentration (40u202fmgNO3--Nu202fL-1), by varying hydraulic retention time (HRT) during different trials from about 14 to 3u202fh. The system was able to achieve almost complete removal of nitrate (>95%) and Total Nitrogen (TN) (>92%) at NO3- loading rates between 66 and 200u202fgNO3--Nu202fm-3NCCu202fd-1. The first stage reactor achieved lower values of effluent nitrate and nitrite than WHO guidelines for drinking water quality (<11.3u202fmgu202fNO3--Nu202fL-1, and 0.9u202fmgNO2--Nu202fL-1, respectively) up to a nitrate loading rate of 167u202fgNO3--Nu202fm-3NCCu202fd-1; in these conditions the second stage acted mainly as polishing step. From a loading rate of 200u202fgNO3--Nu202fm-3NCCu202fd-1 on, N2O accumulation was observed in the first stage reactor, afterwards successfully removed in the second stage. Maximum nitrate removal rate of the 2-step process was 259.83u202fgNO3--Nu202fm-3NCC at HRT of 3.19u202fh. The specific energy consumption of the system (SEC) decreased with decreasing HRT, both in terms of mass of nitrate removed (SECN) and volume treated (SECV). The described combination of two bioelectrochemical systems system hence proved to be effective for groundwater denitrification.

Long-term operation of a novel electrically-enhanced biomass concentrator reactor for wastewater treatment

Membrane biological reactors (MBRs) are a key technology in wastewater treatment nowadays. However, due to their high construction cost and energetic requirements, alternatives based on the same principle of biomass retention have been designed and operated. Amongst these, biomass concentrator reactors (BCRs), using a coarser filter medium instead of a membrane, have shown to be able to remove a wide range of contaminants from wastewater and groundwater. A new BCR-derived technology enhanced with an electric field, called the electrically-enhanced biomass concentrator reactor (E2BCR), was designed and tested for urban wastewater treatment at different organic loads for a period of 180 days. The electrically-enhanced reactor showed better chemical oxygen demand (COD) removal performances than a non-enhanced control reactor (92.4% and 83.6% respectively) thanks also to electrocoagulation effects, and a lower fouling tendency, and proved to be more energy efficient in comparison with the control reactor in terms of energy consumption per mass of COD removed.