Biochar from recovered cellulose as new admixture in constructed wetlands for micropollutant removal: A circular approach.

This study aimed to evaluate the suitability of biochar produced by pyrolysis from recovered wastewater cellulose and activated biologically as an admixture in Constructed Wetlands (CWs) when applied as a post-treatment step to remove micropollutants (MPs) from municipal wastewater effluent. Two planted vertical flow mesocosm CWs with cellulose-based admixtures of different origins (plant residue and recovered toilet paper) were fed with a municipal wastewater effluent representative for rural catchments. The results showed an average MPs elimination of 89.1 % for the activated biochar produced from recovered cellulose when 15 relevant compounds are considered and a reduction of the risk from compounds cocktail below the maximum acceptable level having diclofenac, carbamazepine, PFOS, ciprofloxacin and clarithromycin as main risk drivers (Risk Quotient > 1). The implementation of a circular approach to reduce MPs was finally conducted for the Blies catchment (Saarland region in Germany) characterized by low population density and small, sensitive water bodies. This approach demonstrates the feasibility of combining cellulose recovery with a fine sieve in large wastewater treatment plants (WWTPs) and providing biochar produced from recovered cellulose as an admixture to small WWTP where CW is an affordable solution for MP mitigation.

Valorization of UWWTP effluents for ammonium recovery and MC elimination by advanced AOPs.

The main objective of this study was to generate ready-to-use revalorized irrigation water for fertilization from urban wastewater treatment plant (UWWTP) effluents. The focus was on controlled retention of NH4+ and microcontaminants (MC), using nanofiltration. Retentates generated were treated by solar photo-Fenton at circumneutral pH using Ethylenediamine-N, N'-disuccinic acid (EDDS) iron complexing agent. Solar photo-Fenton degradation efficacy was compared with electrooxidation processes as anodic oxidation, solar-assisted anodic oxidation, electro-Fenton and solar photoelectro Fenton. Finally, phytotoxicity and acute toxicity tests were performed to demonstrate the potentially safe reuse of treated wastewater for crop irrigation. Nanofiltration was able to produce a ready-to-use permeate stream containing recovered NH4+. (valuable nutrient). Solar photo-Fenton treatment at circumneutral pH would only be of interest for rapid degradation of contaminants at less than 1 mg/L in nanofiltration retentates. Other alternative tertiary treatments, such as electrooxidation processes, are a promising alternative when a high concentration of MC requires longer process times. Anodic oxidation was demonstrated to be able to eliminate >80% of microcontaminants and solar-assisted anodic oxidation significantly reduced the electricity consumption. Electro-Fenton processes were the least efficient of the processes tested. Phytotoxicity results showed that irrigation with the permeates reduced germination, root development was mainly promoted and shoot development was positive only at low retention rate (concentration factor = 2). Acute and chronic Daphnia magna toxicity studies demonstrated that the permeate volumes should be diluted at least 50% before direct reuse for crop irrigation.

Solar-driven free chlorine advanced oxidation process for simultaneous removal of microcontaminants and microorganisms in natural water at pilot-scale.

Contamination of natural water (NW) by emerging contaminants has been widely pointed out as one of the main challenges to ensure high-quality drinking water. Thus, the effectiveness of a solar-driven free chlorine advanced oxidation process simultaneously investigating the elimination of six organic microcontaminants (OMCs) and three bacteria from NW at a pilot-scale was evaluated in this study. Firstly, the solar/free chlorine process was studied at lab-scale using a solar simulator to evaluate the effect of free chlorine concentration (0.5-10 mg L-1) on OMC degradation and generation of toxic oxyanions (e.g., ClO3- ions). Thus, the best free chlorine concentration observed was applied for the simultaneous removal of OMCs and pathogens under natural solar light at pilot scale. At lab-scale, the solar/free chlorine (2.5 mg L-1) process achieved 80% of total degradation in 5 min (1.4 kJ L-1 of accumulative UV energy) with an oxidant consumption of 0.3 mg L-1 and without ClO3- generation. Similar results were attained under natural solar irradiation at a pilot-scale. For all bacteria strains, the legally required detection limit (DL = 1 CFU 100 mL-1) for reclaimed water reuse was attained in a short contact time. Still, more importantly, the solar/free chlorine (2.5 mg L-1) process effectively avoided the possible bacterial regrowth in the post-treated sample after six days. Finally, the combination of free chlorine with solar irradiation provided a simple and energy-efficient process for OMC and bacteria removal in NW at a pilot-scale.

Sunlight advanced oxidation processes vs ozonation for wastewater disinfection and safe reclamation.

Solar processes (sunlight/H2O2, solar photo-Fenton with EDDS at neutral pH) were compared to a consolidated technology (ozonation) in the inactivation of target bacteria (E. coli, Salmonella spp. and Enterococcus spp.) under realistic conditions (real secondary treated urban wastewater (WW), pilot scale reactors, natural sunlight) to evaluate their possible industrial application. The highest bacteria inactivation rate (all the target pathogens were inactivated below the detection limit (DL) (100 CFU/100 mL) within 45 min treatment) was observed for ozonation (83 mgO3/L h). Similar inactivation behavior for all bacteria was observed for sunlight/H2O2 (50 mg/L) and solar photo-Fenton (SPF) with EDDS (1:1 molar ratio, 0.1 mM of Fe and 50 mg/L of H2O2). Although the DL was not reached, faster inactivation kinetics (0.007, 0.013 and 0.002 1/min for E. coli, Salmonella spp. and Enterococcus spp., respectively) and lower bacterial concentration after a 180 min treatment were observed for sunlight/H2O2 process compared to SPF (0.005, 0.01 1/min and no inactivation, respectively), Enterococcus spp. being the higher resistance microorganism. The negative effect of carbonates on disinfection performance was also evaluated. Quantitative microbial risk assessment for the ingestion of lettuce irrigated with untreated and treated WW was estimated. Disinfection by ozonation and sunlight/H2O2 processes were found to drastically decrease the associated microbiological risk (the mean risk of illness decreased from 0.10 (untreated) to 1.35 × 10-4 (treated) for E. coli and from 0.03 to 2.21 × 10-6 for Salmonella).

Simultaneous removal of contaminants of emerging concern and pathogens from urban wastewater by homogeneous solar driven advanced oxidation processes.

Simultaneous removal of contaminants of emerging concern and bacteria inactivation in simulated municipal wastewater effluent (SMWW) through solar advanced oxidation processes, namely sunlight/H2O2 and solar photo-Fenton with Ethylenediamine-N,N'-disuccinic acid (EDDS) at neutral pH was investigated. Process efficiency was evaluated in terms of (i) degradation of five contaminants of emerging concern (CECs, namely caffeine, carbamazepine, diclofenac, sulfamethoxazole and trimethoprim) at the initial concentration of 100 µgL-1 each and (ii) bacteria inactivation (E. coli, S. enteritidis and E. faecalis), at the initial concentration of 103 CFU mL-1 each. Solar photo-Fenton process was first investigated at lab scale in a solar simulator to evaluate the effect of iron concentration (0.1 mM and 0.05 mM) and Fe:EDDS ratio (1:2 and 1:1). Subsequently, sunlight/H2O2 and solar photo-Fenton with EDDS (molar ratio 1:1, Fe(III) 0.1 mM) at neutral pH were singularly and sequentially investigated at pilot scale in a raceway pond reactor. Sunlight/H2O2 (50 mg L-1) tests resulted in total bacteria inactivation in 60 min (0.69 kJ L-1) but low CECs removal efficiency. On the opposite, solar photo-Fenton was effective in the removal of the total CECs (87% removal after 20 min and 0.14 kJ L-1) but not in E. faecalis inactivation (the initial concentration did not change even after 180 min). However, when the two processes were operated sequentially, a complete bacteria inactivation was observed in 15 min (0.17 kJ L-1), 20 min (0.23 kJ L-1) and 60 min (0.70 kJ L-1) of treatment for E. coli, S. enteritidis and E. faecalis, respectively and 80% removal of total CECs was achieved after 10 min of Fe:EDDS addition. Sequential combination of sunlight/H2O2 and solar photo-Fenton would be an effective solution for simultaneous CECs removal and bacteria inactivation in the same photo-reactor.