C. Sans

Nitrification, denitrification and biological phosphorus removal in piggery wastewater using a sequencing batch reactor

Nutrients in piggery wastewater with high organic matter, nitrogen (N) and phosphorus (P) content were biologically removed in a sequencing batch reactor (SBR) with anaerobic, aerobic and anoxic stages. The SBR was operated with 3 cycles/day, temperature 30 degrees C, sludge retention time (SRT) 1 day and hydraulic retention time (HRT) 11 days. With a wastewater containing 1500 mg/l ammonium and 144 mg/l phosphate, a removal efficiency of 99.7% for nitrogen and 97.3% for phosphate was obtained. Experiments set up to evaluate the effect of temperature on the process showed that it should be run at temperatures higher than 16 degrees C to obtain good removals (> 95%). Batch tests (ammonia utilization rate, nitrogen utilization rate and oxygen utilization rate) proved to be good tools to evaluate heterotrophic and autotrophic biomass activity. The SBR proved to be a very flexible tool, and was particularly suitable for the treatment of piggery wastewater, characterized by high nutrient content and by frequent changes in composition and therefore affecting process conditions.

Contribution of the ozonation pre-treatment to the biodegradation of aqueous solutions of 2,4-dichlorophenol

The effect of ozonation on the biodegradability of 100-ppm aqueous solutions of 2,4-dichlorophenol has been investigated. BOD at 5, 10 and 21 days, BOD/COD and BOD/TOC ratios and the average oxidation state are presented. Biodegradability measured as BOD5/COD ratio was increased from 0 of the original solution to 0.25 at the moment of removing all the initial compound (corresponding to an ozone dose of 0.12 g L-1, 0.48 for BOD21/COD ratio). To test the effect of this pre-treatment, the biological oxidation of these pre-ozonated solutions was performed in two semi-continuous stirred tank reactors, one with non-acclimated sludge and one with acclimated-to-phenol sludge. The study showed that the TOC content of the pre-treated solution could be removed up to 68% by an aerobic biological treatment as well as co-digested with municipal wastewater (TOC removal up to 82%), with similar operating retention times to a municipal wastewater plant (12-24 h). Kinetic studies based on Monod model have also been carried out. Pseudo-first-order kinetic constants were found to be in the range of 0.5-0.8 L g TVSS-1 h-1.

Effects of ozone pre-treatment on diclofenac: intermediates, biodegradability and toxicity assessment.

Diclofenac (DCF), a common analgesic, anti-arthritic and anti-rheumatic drug, is one of the most frequently detected compounds in water. This study deals with the degradation of diclofenac in aqueous solution by ozonation. Biodegradability (BOD(5)/COD ratio and Zahn-Wellens test), acute ecotoxicity and inhibition of activated sludge activity were determined in ozonated and non-ozonated samples. Liquid chromatography coupled with time-of-flight mass spectrometry (LC/TOF-MS) was used to identify the intermediates formed in 1 h of ozonation. Eighteen intermediates were identified by these techniques and a tentative degradation pathway for DCF ozonation is proposed. Experimental results show that ozone is efficient at removing DCF: >99% removal (starting from an initial concentration of 0.68 mmol L(-1)) was achieved after 30 min of ozonation (corresponding to an absorbed ozone dose of 0.22 g L(-1), which is 4.58 mmol L(-1)). However, only 24% of the substrate was mineralized after 1 h of ozonation. The biodegradability, respiration inhibition in activated sludge and acute toxicity tests demonstrate that ozonation promotes a more biocompatible effluent of waters containing DCF.

Volatile fatty acids production by mesophilic fermentation of mechanically-sorted urban organic wastes in a plug-flow reactor

Volatile fatty acids (VFA) production by anaerobic fermentation of municipal solid wastes was studied at pilot-plant level. A plug-flow reactor (80 l total volume), with and without concentrated sludge recirculation, was employed to digest an organic fraction of the municipal solid waste (OFMSW)-based substrate. This was composed of OFMSW mechanically-selected in a full-scale plant with OFMSW collected from fruit and vegetable markets and mixed in a way to obtain a feed mixture with a proportion of total volatile solids (TVS)/total solids (TS) of 60%. The fermentation process was studied at different retention times (RT) (from 8 h to 8 days) and at very high organic loading rates (OLR) (from 22·4 to 85·2 kg VS/m3 d) at mesophilic temperature (37 ± 2°C). Results showed an increase in VFA production at higher retention times (from 11·8 g/l at 2 days to 23·1 g/l at 6 days RT) when no recirculation was used. VFA production was also high when part of the digested sludge was recirculated (19·5 g/l at 2 days of hydraulic RT and 8 days of solid RT). Acetic and butyric were the acids produced in the largest quantities.

Pharmaceuticals and organic pollution mitigation in reclamation osmosis brines by UV/H2O2 and ozone.

One significant disadvantage of using reverse osmosis (RO) for reclamation purposes is the need to dispose of the RO retentates. These retentates contain a high concentration of micropollutants, effluent organic matter (EfOM) and other inorganic constituents, which are recalcitrant to biological treatment and may impact the environment. The occurrence of 11 pharmaceuticals (concentrations ranging from 0.2 to 1.6 μg L(-1)) and their mitigation in RO retentates by a UV/H2O2 process and ozonation was studied using a wide range of oxidant dosages. Eleven pharmaceuticals were identified at. Initial observed kinetic constants (kobs) were calculated for the different pharmaceuticals. Other typical wastewater parameters were also monitored during the UV/H2O2 and ozonation reactions. The range for kobs was found to be 0.8-12.8L mmol O3(-1) and 9.7-29.9 L mmol H2O2(-1) for the ozonation and UV/H2O2 process, respectively. For ozonation, Atenolol, Carbamazepine, Codeine, Trimethoprim and Diclofenac showed the lowest initial kobs (in the order mentioned). Atenolol and Carbamazepine appeared as the most ozone resistant pharmaceuticals, exhibiting the lowest percentage of elimination at low ozone doses. On the other hand, despite the non-selectivity of HO, differences in the initial kobs were also observed during the UV/H2O2 process. Trimethoprim, Paroxetine and Sulfamethoxazole exhibited the lowest initial kobs values (in the order mentioned). Trimethoprim and Paroxetine also exhibited the lowest percentage removal when low H2O2 doses were assayed. The compounds that were identified as problematic during ozonation were more efficiently removed by the UV/H2O2 process. UV/H2O2 generally appeared to be a more efficient technology for removing pharmaceuticals from RO brines compared to ozonation.

Acidogenic fermentation of organic urban wastes in a plug-flow reactor under thermophilic conditions

Abstract The acidogenic fermentation of the organic fraction of municipal solid wastes (OFMSW) was studied at thermophilic temperature conditions (55 ± 2°C) in a 80 l plug-flow reactor. In particular, volatile fatty acids (VFA) production and individual acid distribution was monitored at different hydraulic retention times (HRT) (from 2 to 6 days HRT). The feed mixture was composed of OFMSW mechanically selected in a full-scale plant and OFMSW collected from a fruit and vegetables market, with TS content around 25% and a ratio of total volatile solids (TVS)/total solids (TS) of 60%. When inoculum was added to the feed mixture, the thermophilic acidogenic fermentation of the OFMSW became a feasible process for obtaining VFA. The maximum VFA concentration obtained was 19·6 g/l at 6 days retention time, although VFA production at short hydraulic retention time (8–16 h) was already important. VFA production was distributed in all individual acids, but mainly acetic and butyric acids.

Ozonation of NSAID: A Biodegradability and Toxicity Study

This work deals with the biodegradability and toxicity of three non-steroidal anti-inflammatory drugs (NSAID) (diclofenac, ibuprofen and naproxen) treated by ozonation. The results show that the total removal of 200 mg L−1 of diclofenac and 100 mg L−1 of naproxen is possible using an ozone dose of 0.20 and 0.04 g L−1, respectively. For 200 mg L−1 of ibuprofen, 90% removal is achieved using an ozone dose of 2.3 g L−1. The BOD5/COD ratio, the Zahn-Wallens test and EC50 toxicity test (Microtox) are chosen as biological and toxicity indicators of NSAID intermediates. The evolution of BOD5/COD ratio during 1 hour of treatment is evaluated and the results show that ozonation improves the biodegradability for the three NSAID treated solution. The Zahn-Wellens test for diclofenac and ibuprofen solutions shows that biological mineralization, after 28 days, is higher for diclofenac than for ibuprofen solution. According to the Microtox test, the treatment with ozone removes the toxicity of the naproxen solution. Taking into account the results obtained with the biocompatibility tests it could be assumed that ozonation is an adequate treatment for removal NSAID in aquatic medium, and the ozonated effluents could be post-treated in a biological wastewater facility.

Chemicals production from wastes

Abstract In this paper the results of volatile fatty acids (VFA) production from the hydrolysis of fruit and vegetable wastes are presented. Experiments were conducted at laboratory scale reactors (130 cm3). pH was controlled at the desired level in order to study its influence. High yields were obtained (up to 40 g VFA 1−1) at the optimum pH, which resulted in the range of 6.4–6.6. A first order kinetic model fitted quite well to the degradation rate. A mathernathical expression relating the first order kinetic constant with pH was also deduced.

Role of oxygen and DOM in sunlight induced photodegradation of organophosphorous flame retardants in river water

The wide use of organophosphorous flame retardants (OPFR) and plasticizers causes a continuous release of large quantities into natural waters. One of the main contributors to micropollutants depletion in surface water is sunlight induced phototransformations. This study aims to elucidate whether alkyl, chloroalkyl and aryl organophosphorus flame retardants undergo phototransformations in river water. To perform the experiments, nine OPFR were subjected to natural sunlight, Xe lamp (simulated sunlight) and UV-C irradiations in ultra-pure Milli-Q water, Milli-Q water with humic acid and river water. Experiments demonstrated that OPFR achieve an important degree of photodegradation noticeable at long irradiation time, although direct photolysis did not account as the main photodegration mechanism. Results indicated that sunlight absorbing OPFR exhibited photosensitizing activity. The presence of azide in ultra- pure water inhibited some OPFR photodegration by singlet oxygen (1O2) scavenging, and the absence of dissolved oxygen significantly depleted most of OPFR removal. In the conditions studied, humic acid inhibited OPFR phototransformations, while river water enhanced their removal. Results from this study point out the need to further investigate the role of some OPFR as photosensitizers, which are important for fate and ecological risk assessment of flame retardants and other micropollutants in water.

Comparison between Ozonation and Photo-Fenton Processes for Pesticide Methomyl Removal in Advanced Greenhouses

So-called “Advanced Greenhouses” are a new approach to the concept of protected agriculture. Among other technological and structural improvements, these facilities give the possibility of recycling the irrigation surplus water, rich in lixiviates, salts, pesticides and its metabolites. After many cycles, the current is so concentrated on those substances that it becomes necessary for the presence of a membrane separation stage which brine, highly concentrated on those named pollutants, has to be treated before being sent to the public sewage system. Advanced Oxidation Processes, among other chemical treatments, can be considered an alternative to process this current effluent. In this work, concentrated aqueous solutions of methomyl as model pesticide (200 mg·L−1) have been subjected to two of those processes: ozonation and photo-Fenton reaction. Analysis of the elimination of the pesticide itself and the grade of mineralization achieved have shown how, while the ozonation is the most effective process decomposing the pesticide (eliminating the total concentration in 60 minutes), the photo-Fenton reaction mineralizes successfully the 40% of the total organic load (the ozonation only can cope with 20%) but only decompose a 40% of the pesticide. Evolution of biodegradability and toxicity of the effluent along both processes was also analyzed. Intermediates generated both by ozonation and photo-Fenton did not increase the biodegradability of the treated effluents. Nevertheless, while acute toxicity just after 15 minutes of treatment with ozone is notably higher than for raw solution, and it is maintained till the end of the experiment (120 min), though, toxicity along photo-Fenton reaction has two growing and decreasing regions, always shows lower values than the provoked during ozonation. None of the two assayed processes has been proved to increase biocompatibility of highly concentrated methomyl solutions.