Influence of Carbon Source on the Efficiency of Nitrogen Removal and Denitrifying Bacteria in Biofilm from Bioelectrochemical SBBRs

Environmental pollution removal using electrostimulation of microorganisms by alternative current

The entrance of some toxic and hazardous chemical agents such as antibiotics, pesticides, and herbicides into the environment can cause various problems to human health and the environment. In recent years, researchers have considered the use of electrostimulation in the processes of microbial metabolism and biological systems for the treatment of pollutants in the environment. Although several electrostimulation reports have been presented for pollutant removal, little attention has been paid to alternative current (AC) biostimulation. This study presents a systematic review of microbial electrostimulation using bioelectrochemical systems supplied with AC. The utilization of alternating current bioelectrochemical systems (ACBESs) has some advantages such as the provide of appropriate active biofilms in the electrodes due to the cyclical nature of the current and energy transfer in an appropriate manner on the electrode surfaces. Moreover, the ACBESs can reduce hydraulic time (HRT) under optimal conditions and reduce the cost of converting electricity using AC. In microbial electrostimulation, amplitude (AMPL), waveform, C/N, and current have a significant effect on increasing the removal efficiency of the pollutants. The obtained results of the meta-analysis illustrated that various pollutants such as phenol, antibiotics, and nitrate have been removed in an acceptable range of 96% using the ACBESs. Therefore, microbial electrostimulation using AC is a promising technology for the decomposition and removal of various pollutants. Moreover, the ACBESs could provide new opportunities for promoting various bioelectrochemical systems (BESs) for the production of hydrogen or methane.

Technological Parameters of Rotating Electrochemical and Electrobiological Disk Contactors Depending on the Effluent Quality Requirements

Soilless tomato cultivation wastewater, with typically low COD, high concentrations of phosphorus, and oxidized forms of nitrogen, may be effectively treated in a rotating electrochemical disk contactor (RECDC) and in a bioelectrochemical reactor (BER), such as a rotating electrobiological disk contactor (REBDC). The aim of this study was to determine the technological parameters of both reactors, i.e., electric current density (J) and hydraulic retention time (HRT), depending on the effluent quality requirements. The study was conducted with four one-stage RECDCs and with four one-stage REBDCs, at four hydraulic retention times, i.e., 4, 8, 12, and 24 h, and electric current densities of 0.63, 1.25, 2.50, 5.00, and 10.00 A/m2. It was demonstrated that soilless tomato cultivation wastewater could be effectively treated in electrochemical and electrobiological disk contactors, and then discharged to sewage system facilities. In a RECDC, the highest denitrification (53.4%) and dephosphatation (99.8%) performance was achieved at J = 10.0 A/m2 and HRT = 24 h. If the effluents are to be discharged to natural reservoirs, their effective treatment is only feasible in a REBDC. The bioelectrochemical disk contactor ensured over 90% dephosphatation effectiveness. At HRT = 24 h and all electric current densities studied, the concentrations of pollutants in the effluent met requirements set for industrial wastewater discharged into natural waters and the ground. By applying J = 2.5 A/m2 and HRT = 24 h in the REBDC, it was possible to achieve a phosphorus concentration below 3.0 mg P/L and concentrations of ammonia nitrogen and nitrites lower than the permissible levels for treated industrial wastewater introduced to waters and to the ground. Given the nitrate concentration (exceeding 30 mg N/L), an external carbon source is recommended to aid a treatment process that uses a technological system with a REBDC. Technological schemes were proposed for wastewater treatment plants (WWTPs) with a RECDC and a REBDC, for discharging treated wastewater to natural waters, the ground, and sewage systems.

Application of Internal Carbon Source from Sewage Sludge: A Vital Measure to Improve Nitrogen Removal Efficiency of Low C/N Wastewater

Biological nitrogen removal from wastewater is widely used all over the world on account of high efficiency and relatively low cost. However, nitrogen removal efficiency is not optimized when the organic matter has inadequate effect for the lack of a sufficient carbon source in influent. Although addition of an external carbon source (e.g., methanol and acetic acid) could solve the insufficient carbon source problem, it raises the operating cost of wastewater treatment plants (WWTPs). On the other hand, large amounts of sludge are produced during biological sewage treatment, which contain high concentrations of organic matter. This paper reviews the emerging technologies to obtain an internal organic carbon resource from sewage sludge and their application on improving nitrogen removal of low carbon/nitrogen wastewater of WWTPs. These are methods that could solve the insufficient carbon problem and excess sludge crisis simultaneously. The recovery of nitrogen and phosphorus from treated sludge before recycling as an internal carbon source should also be emphasized, and the energy and time consumed to treat sludge should be reduced in practical application.

Investigation on the improved electrochemical and bio-electrochemical treatment processes of soilless cultivation drainage (SCD)

The soilless crop cultivation under cover generates wastewater called soilless cultivation drainage (SCD), being a nutrient-rich overflow. The average concentration of phosphorus- and nitrogen-based pollutants from soilless tomato cultivation usually ranges from 35.4 to 104.0 mg P/L and from 270.0 to 614.9 mg N/L, respectively. In bio-electrochemical reactors, nitrogen and phosphorus are removed via biological denitrification, electrochemical nitrate reduction, bio-electrochemical reduction, and electrocoagulation. The novelty of this study is due to the use of alternating current (AC), which can both mitigate the corrosion on the anode and solve the issue of insoluble oxide build-up on the cathode. Additionally, and crucially, it promotes bacterial growth and activity. The aim of the present study was to determine (1) the effectiveness of soilless cultivation drainage treatment methods that employ biological and electrochemical processes, with consideration given to (2) the quantity and quality of the produced sludge as a potential nutrient-rich product. The bio-electrochemical reactor proved more effective than the electrochemical one and ensured a high TP and TN removal efficiency exceeding 97% and 66%, respectively. The resulting sludge was rich in such elements as calcium, potassium, carbon, phosphorus, and nitrogen, and as such may serve as a viable alternative to conventional mineral fertilizers.

Sustainable soil amendments to improve nature-based solutions for wastewater treatment and resource recovery

Vegetation Filters (VFs) can be a sustainable solution to treat wastewater and to recover resources such as nutrients, water and biomass from small municipalities and isolated dwellings. However, under certain conditions, the leakage of nutrients, especially of nitrate, can represent a limitation. The addition of two sustainable soil amendments, woodchips and biochar, has been tested as a strategy to improve nutrient attenuation in VFs increasing sorption sites and microbial activity. To this end, unsaturated infiltration and batch experiments have been carried out at laboratory scale. The systems for infiltration experiments contain natural soil, natural soil amended with woodchips and natural soil amended with biochar. To determine the sorption capacity of NH₄⁺, batch tests were performed using an amendment/SWW ratio of 1:20 and an NH₄⁺ initial concentration ranging from 30 to 600 mg L^-1. Results from the infiltration experiments show a high attenuation (~95%) of total phosphorous (TP) independently of the amendments. Different behaviour is observed for total nitrogen (TN). The removal of this species is obtained only in the soil amended with woodchips (>85%) whereas the natural soil alone and the soil with biochar have no impact on TN attenuation. In these two porous media, all the NH₄⁺ input concentration is transformed to NO₃^- that infiltrates without further reactions. According to batch experiment results, the potential role of biochar in the nutrient attenuation is limited to sorption processes (K_d (NH₄⁺) = 21.37-193.18 L kg^-1). Woodchips act primarily as a labile source of carbon promoting biodegradation, being more effective for nutrient attenuation than the sorption capacity of biochar.

Electric Power Consumption and Current Efficiency of Electrochemical and Electrobiological Rotating Disk Contactors Removing Nutrients from Wastewater Generated in Soil-Less Plant Cultivation Systems

The study was conducted in a one-stage rotating electrobiological disk contactor (REBDC) and a rotating electrochemical disk contactor (RECDC). Synthetic wastewater with characteristics similar to the wastewater from soil-less cultivation of tomatoes was used in the experiment. Current efficiency (CE) values, that express the denitrification performance of bio- and electrochemical reactors, were higher in the electrobiological contactor than in the electrochemical one. Combining biological processes with electrochemical processes in the electrobiological contactor resulted in almost 20% higher current efficiency in the contactor operated at a density of 0.63 A/m2 and hydraulic retention time (HRT) = 4 h. The study showed that, in both the electrochemical and the electrobiological contactor, current density increase and hydraulic retention time extension increased electric power consumption (E) during phosphorus compounds removal and simultaneously lowered current efficiency.

Alicycliphilus: current knowledge and potential for bioremediation of xenobiotics

Alicycliphilus is a promising candidate for participating in the development of novel xenobiotics bioremediation processes. Members of the Alicycliphilus genus are environmental bacteria mostly found in polluted sites such as landfills and contaminated watercourses, and in sewage sludges from wastewater treatment plants. They exhibit a versatile metabolism and the ability to use oxygen, nitrate and chlorate as terminal electron acceptors, which allow them to biodegrade xenobiotics under oxic or anoxic conditions. Pure cultures of Alicycliphilus strains are able to biodegrade some pollutants such as industrial solvents (acetone, cyclohexanol and N-methylpyrrolidone), aromatic hydrocarbons (benzene, toluene and anthracene), as well as polyurethane varnishes and foams, and they can even transform Cr(VI) to Cr(III). In addition, Alicycliphilus has also been identified in bacterial communities involved in wastewater treatment plants for denitrification, and the degradation of emerging pollutants such as triclosan, nonylphenol, N-heterocyclic aromatic compounds (indole and quinoline), and antibiotics (tetracycline and oxytetracycline). This work summarizes the current knowledge on the Alicycliphilus genus, describing its different metabolic characteristics, focusing on its xenobiotic biodegradation abilities and examining the distinct pathways and molecular bases that sustain them. We also discuss the progress made in genetic manipulation and 'omics' analyses, as well as Alicycliphilus participation in novel bioremediation strategies.