F. Omil

Removal of pharmaceutical and Personal Care Products (PPCPs) under nitrifying and denitrifying conditions.

The contribution of volatilization, sorption and transformation to the removal of 16 Pharmaceutical and Personal Care Products (PPCPs) in two lab-scale conventional activated sludge reactors, working under nitrifying (aerobic) and denitrifying (anoxic) conditions for more than 1.5 years, have been assessed. Pseudo-first order biological degradation rate constants (k(biol)) were calculated for the selected compounds in both reactors. Faster degradation kinetics were measured in the nitrifying reactor compared to the denitrifying system for the majority of PPCPs. Compounds could be classified according to their k(biol) into very highly (k(biol)>5Lg(SS)(-1)d(-1)), highly (1<k(biol)<5Lg(SS)(-1)d(-1)), moderately (0.5<k(biol)<1Lg(SS)(-1)d(-1)) and hardly (k(biol)<0.5Lg(SS)(-1)d(-1)) biodegradable. Results indicated that fluoxetine (FLX), natural estrogens (E1+E2) and musk fragrances (HHCB, AHTN and ADBI) were transformed to a large extent under aerobic (>75%) and anoxic (>65%) conditions, whereas naproxen (NPX), ethinylestradiol (EE2), roxithromycin (ROX) and erythromycin (ERY) were only significantly transformed in the aerobic reactor (>80%). The anti-depressant citalopram (CTL) was moderately biotransformed under both, aerobic and anoxic conditions (>60% and >40%, respectively). Some compounds, as carbamazepine (CBZ), diazepam (DZP), sulfamethoxazole (SMX) and trimethoprim (TMP), manifested high resistance to biological transformation. Solids Retention Time (SRT(aerobic) >50d and <50d; SRT(anoxic) >20d and <20d) had a slightly positive effect on the removal of FLX, NPX, CTL, EE2 and natural estrogens (increase in removal efficiencies <10%). Removal of diclofenac (DCF) in the aerobic reactor was positively affected by the development of nitrifying biomass and increased from 0% up to 74%. Similarly, efficient anoxic transformation of ibuprofen (75%) was observed after an adaptation period of 340d. Temperature (16-26 degrees C) only had a slight effect on the removal of CTL which increased in 4%.

Pre-treatment of hospital wastewater by coagulation-flocculation and flotation

Coagulation-flocculation and flotation processes were evaluated for the pre-treatment of hospital wastewater, including the removal of 13 pharmaceutical and personal care products (PPCPs). Coagulation-flocculation assays were performed in a Jar-Test device and in a continuous pilot-scale plant. Raw hospital wastewater as well as the effluent from the continuous coagulation plant were treated in a flotation cell. Removal of total suspended solids (TSS) during pre-treatment was very effective, reaching an average removal efficiency of 92% in the combined coagulation-flotation process. Musk fragrances were eliminated to a high degree during batch coagulation-flocculation (tonalide: 83.4+/-14.3%; galaxolide: 79.2+/-9.9%; celestolide: 77.7+/-16.8%), presumably due to their strong lipophilic character which promotes the interaction of these compounds with the lipid fraction of solids. For diclofenac (DCF), naproxen (NPX) and ibuprofen (IBP) maximum removals of 46%, 42% and 23%, respectively, were obtained, while the rest of PPCPs were not affected by the physico-chemical treatment. Flotation of raw wastewater led to slightly worse results compared to coagulation-flocculation, although the combined action of both improved the overall efficiency of the process. The proposed pre-treatment strategy for hospital wastewater is useful for assimilating its conventional physico-chemical characteristics to that of municipal wastewater as well as for reducing the load of some PPCPs into the sewer system.

Comparison of predicted and measured concentrations of selected pharmaceuticals, fragrances and hormones in Spanish sewage

A review of consumption and excretion rates of 17 pharmaceuticals, two musk fragrances and two hormones by the Spanish population in 2003 was performed. For that purpose, three different models were used: (i) extrapolation of the per capita use in Europe to the number of inhabitants of Spain for musk fragrances; (ii) annual prescription items multiplied by the average daily dose for pharmaceuticals and; (iii) excretion rates of different groups of population for hormones. This information enabled the prediction of the expected concentrations (PEC) entering sewage treatment plants (STPs), which were subsequently compared with the measured environmental concentrations (MEC) in raw sewage. Annual drugs consumption in Spain ranges from few kilograms (Oxazepam and 17alpha-ethinylestradiol) to several hundred of tons (Ibuprofen). The quantities of musks used accounts for 110-450 kg d(-1) and the total amount of hormones excreted daily reaches almost 1 kg d(-1). 12 out of 21 selected substances were predicted to be present in raw sewage influent at concentrations greater than 100 ng l(-1) and these predicted concentrations fitted with the measured values for half of them (Carbamazepine, Diazepam, Ibuprofen, Naproxen, Diclofenac, Sulfamethoxazole, Roxithromycin, Erythromycin and 17alpha-ethinylestradiol).

Anaerobic hydrolysis and acidogenesis of wastewaters from food industries with high content of organic solids and protein

Abstract The anaerobic hydrolysis and acidification of wastewaters rich in organic suspended solids and protein was studied in continuous stirred reactors. The effluents employed in this study were obtained from a fish meal factory (30–120 g COD/l, 5–40 g VSS/l, 10–30 g protein/l). The effect of stirring on the anaerobic biodegradability was initially determined and, on the basis of these results, the hydrolysis–acidification step was optimised in terms of temperature and HRT. Thermophilic (55°C) and mesophilic (37°C) reactors were operated at HRT ranging from 6 to 48 h. No nutrients were added, and pH remained in the range 7.2–7.7 due to the high alkalinity. Extremely high organic loading rates (OLR) were applied (up to 400 kg COD/m 3 d) with no significant methane production, obtaining maximum efficiencies of 44% for acidification, 58% for VSS removal and 80% for protein removal at 55°C and 24 h of HRT. However, acidification (2 kg COD-VFA/m 3 h) and VSS removal rates (0.4 kg VSS r /m 3 h) were maximum at HRT of 12–24 h, operating at the same temperature. Most of protein was converted into VFA and ammonia, even when working at the lowest HRT. As a consequence, the content of total ammonia in these reactors reached extremely high values in both cases (15–17 g N-TA/l), which implies high concentrations of free ammonia (up to 0.66 g N-FA/l at 37°C and 1.64 g N-FA/l at 55°C), these differences being due to the effect of temperature on the dissociation equilibrium. Although a more efficient operation was achieved at 55°C, mesophilic operation is recommended if a two-phase system was considered for the overall treatment of these effluents, since toxic effects from free ammonia would impede a stable operation in the methanogenic reactor at thermophilic conditions.

Effect of upward velocity and sulphide concentration on volatile fatty acid degradation in a sulphidogenic granular sludge reactor

During anaerobic treatment of sulphate-containing wastewaters, sulphate-reducing bacteria (SRB) compete with methane-producing bacteria (MPB) for the available electron-donors. In this work, the anaerobic treatment of a synthetic wastewater, consisting of a mixture of acetate, propionate and butyrate and high concentrations of sulphate (COD: sulphate ratio 0·5) was studied in an upflow anaerobic granular sludge bed reactor. The influence of the superficial upward liquid velocity (vup), the influent composition and reactor pH on the competition between SRB and MPB was investigated. At a vup of 2 m h−1 and pH 8, 93–97% of the COD was degraded by SRB. With increasing vup-values, COD removal efficiencies decreased, while at a vup of 6 m h−1 the fraction of COD removed by MPB rose to 23%. Elevation of the influent acetate concentrations, by decreasing the vup (lower recirculation) or by the use of an influent volatile fatty acid mixture with a higher acetate content, resulted in an increase of methanogenesis up to 41% of the total COD removal. In contrast, elevated levels of propionate and butyrate in the influent favoured the sulphate reducing process. A decrease of pH from 8 to 7 resulted in free hydrogen sulphide concentrations higher than 200 mg litre−1. This strongly inhibited methanogenesis while SRB were hardly affected, with a subsequent decrease of the COD removed by MPB from 41 to 7% as a result.

Influence of nitrifying conditions on the biodegradation and sorption of emerging micropollutants

High biodegradation efficiencies of different emerging micropollutants were obtained with nitrifying activated sludge (NAS) working at high nitrogen loading rates (NLR), that boosted the development of biomass with high nitrifying activities (>1 g N-NH(4)(+)/g VSS d). Come-tabolic biodegradation seemed to be responsible for the removal of most compounds due to the action of the ammonium monooxygenase enzyme. NAS showed a different affinity for each compound, probably due to steric hindrance, activation energy limitations or the presence of specific functional groups. Increasing loading rates of micropollutants were removed at shorter hydraulic retention times, although the biodegradation efficiencies of compounds with slow/intermediate kinetics, such as fluoxetine, erythromycin, roxithromycin and trimethoprim, diminished due to kinetic and/or stoichiometric limitations. Solids retention time, always above the minimum to avoid the washout of nitrifiers, did not enhance the biodegradation of any of the selected compounds, with the exception of diclofenac. Regarding sorption, the solid-liquid distribution coefficients (K(d)) obtained in NAS were very similar to those found in conventional activated sludge by other authors. No correlation between K(d) values and any of the operational parameters was found for the selected substances.

Long-term competition between sulfate reducing and methanogenic bacteria in UASB reactors treating volatile fatty acids

The competition between acetate utilizing methane-producing bacteria (MB) and sulfate-reducing bacteria (SRB) was studied in mesophilic (30 degrees C) upflow anaerobic sludge bed (UASB) reactors (upward velocity 1 m h-1; pH 8) treating volatile fatty acids and sulfate. The UASB reactors treated a VFA mixture (with an acetate:propionate:butyrate ratio of 5:3:2 on COD basis) or acetate as the sole substrate at different COD:sulfate ratios. The outcome of the competition was evaluated in terms of conversion rates and specific methanogenic and sulfidogenic activities. The COD:sulfate ratio was a key factor in the partitioning of acetate utilization between MB and SRB. In excess of sulfate (COD:sulfate ratio lower than 0.67), SRB became predominant over MB after prolonged reactor operation: 250 and 400 days were required to increase the amount of acetate used by SRB from 50 to 90% in the reactor treating, respectively, the VFA mixture or acetate as the sole substrate. The competition for acetate was further studied by dynamic simulations using a mathematical model based on the Monod kinetic parameters of acetate utilizing SRB and MB. The simulations confirmed the long term nature of the competition between these acetotrophs. A high reactor pH (+/-8), a short solid retention time (<150 days), and the presence of a substantial SRB population in the inoculum may considerably reduce the time required for acetate-utilising SRB to outcompete MB.

Anaerobic treatment of saline wastewaters under high sulphide and ammonia content

The anaerobic treatment of wastewaters from the seafood-processing industry was studied in a 15 m3 industrial pilot-plant. These effluents have a high organic content (10–60 g COD/litre), with protein percentages between 25 and 70%, and a salinity similar to sea water: sodium (5–12 g/l), chloride (8–19 g/l) and sulphate (0·6–2·7 g/l). This high concentration of salts, together with the production of sulphide and ammonia due to sulphate reduction and protein breakdown, respectively, produces important inhibitory/toxic effects on non-adapted biomass. A mixture of anaerobic sludges from the treatment of non-saline wastewaters was used as the inoculum. After an initial start-up procedure, where the acclimation of the biomass was the objective, 70–90% organic matter removal was achieved, operating at dissolved sulphide (DS), total ammonia (TA) and sodium concentrations in the ranges of 0·25–0·5 g S-DS/l, 1·0–3·0 g N-TA/l and 6–10 g/l, respectively. The adaptation of the biomass to the salinity and the antagonistic effects on sodium toxicity caused by the presence of other ions made it possible to operate at these high sodium concentrations. Due to the strong buffering capacity of the process, pH was maintained above 7·25, resulting in levels of free hydrogen sulphide (FS) that were lower than 100 mg S-FS/l, which were not high enough to produce inhibition effects on adapted sludges. However, the control of the influent protein content is necessary, since values higher than 200 mg N-FA/l of free ammonia (FA) were shown to be inhibitory for this process.

Anaerobic filter reactor performance for the treatment of complex dairy wastewater at industrial scale

The wastewaters discharged by raw milk quality control laboratories are more complex than the ones commonly generated by dairy factories because of the presence of certain chemicals such as sodium azide or chloramphenicol, which are used for preserving milk before analysis. The treatment of these effluents has been carried out in a full-scale plant comprising a 12 m(3) anaerobic filter (AF) reactor and a 28 m(3) sequential batch reactor (SBR). After more than 2 years of operation, a successful anaerobic treatment of these effluents was achieved, without fat removal prior to the anaerobic reactor. The organic loading rates maintained in the AF reactor were 5-6 kg COD/m(3) d, with COD removal being higher than 90%. No biomass washout was observed, and most of the fat contained in the wastewaters was successfully degraded. The addition of alkalinity is crucial for the maintenance of a proper buffer medium to ensure pH stability. The effluent of the AF reactor was successfully treated in the SBR reactor, and a final effluent with a COD content below 200 mg/l and total nitrogen below 10mg N/l was obtained.

The effect and fate of antibiotics during the anaerobic digestion of pig manure

This work studies the inhibitory effects and fate of the antibiotics oxytetracycline (OTC) and chlortetracycline (CTC) during the anaerobic digestion of pig manure. Both substances were added together in batch assays at concentrations of 10, 50 and 100mgL(-1). Control assays only with antibiotics (abiotic) as well as without antibiotics (biotic) were also conducted. Methane production was reduced by 56%, 60% and 62% at OTC and CTC concentrations of 10, 50 and 100mgL(-1), respectively. The IC(50) level calculated from these experiments was estimated to be around 9mgL(-1), a significant value considering the reported concentrations of these compounds in pig manure samples (up to 136mgL(-1)). Strong adsorption to solid matter was observed, which increased the stability of both substances. Antibiotic degradation was thus much higher in control assays, without solids, than those determined from assays including inoculum and manure substrate.