D. Sales

The effect of temperature on the biodegradation of a nonylphenol polyethoxylate in river water

Abstract In this paper a study is made of the biodegradability of a non-ionic surfactant, a nonylphenol polyethoxylate, in river water by means of monitoring the residual surfactant matter and the metabolites that may be generated. The influence of temperature on the extent of primary and ultimate biodegradation, and the kinetics of degradation are also determined. The method used was the river die-away test, and the biodegradation process was monitored by normal and reversed phase high-performance liquid chromatography (HPLC). These results are supported by other indirect measurements and indicators of the existence of microbial degradation process, as well as the parameters for the control of the process. The results obtained indicate that temperature has a strong influence on the period of acclimation of the microorganisms and on the rate of biodegradation. The percentages of primary biodegradation vary from 68% at 7°C to 96% at 25°C, and at all the temperatures studied, metabolites are generated during the biodegradation process which do not totally disappear at the end of the assay. The percentages of mineralization reached in the various assays, ranging from 30% at 7°C to 70% at 25°C, also show the great influence of temperature. Finally, a kinetic study of the biodegradation process has been carried out, with excellent fit of the experimental data to the kinetic model of Quiroga and Sales.

Analysis of methanogenic activity in a thermophilic-dry anaerobic reactor: Use of fluorescent in situ hybridization

Methanogenic activity in a thermophilic-dry anaerobic reactor was determined by comparing the amount of methane generated for each of the organic loading rates with the size of the total and specific methanogenic population, as determined by fluorescent in situ hybridization. A high correlation was evident between the total methanogenic activity and retention time [-0.6988Ln(x)+2.667] (R(2) 0.8866). The total methanogenic activity increased from 0.04x10(-8) mLCH(4) cell(-1)day(-1) to 0.38x10(-8) mLCH(4) cell(-1)day(-1) while the retention time decreased, augmenting the organic loading rates. The specific methanogenic activities of H(2)-utilizing methanogens and acetate-utilizing methanogens increased until they stabilised at 0.64x10(-8) mLCH(4) cell(-1)day(-1) and 0.33x10(-8) mLCH(4) cell(-1)day(-1), respectively. The methanogenic activity of H(2)-utilizing methanogens was higher than acetate-utilizing methanogens, indicating that maintaining a low partial pressure of hydrogen does not inhibit the acetoclastic methanogenesis or the anaerobic process.

Thermophilic Anaerobic Degradation of Distillery Wastewater in Continuous-Flow Fluidized Bed Bioreactors

This paper reports and discusses a laboratory experiment that tested the anaerobic fluidized bed (AFB) technology as a means for the treatment of concentrated industrial wastewater (wine distillery, vinasses) at thermophilic conditions. The purposes were to operate and characterize AFB under high organic loading conditions and to report on their steady‐state performance. Experimentally, it was confirmed that AFB systems can achieve >82.5% chemical oxygen demand (COD) reduction at a COD loading of 32.3 kg of COD m−3 day−1 for treating vinasses of wine. At hydraulic retention time (HRT) of 0.46 day, the volumetric rate of methane generation was 5.8 m3 of CH4 m−3 day−1 with a methane yield of 0.33 m3 of CH4/kg of COD removal. The greatest efficiency of substrate removal was 97% for an organic loading rate of 5.9 kg of COD m−3 day−1 and HRT of 2.5 days. The food‐to‐microorganism (F:M) ratio can be used as a parameter for treatment performance evaluation of AFB. For vinasses, excellent COD reduction and methane production were achievable at the F:M ratio of 0.55 kg of COD kg−1 VSatt day−1 (more than 80% of feed COD was removed, and 9 m3 m−3 day−1 of methane was produced).

Levels of linear alkylbenzenesulfonate (LAS) in waters and sediments of the coastal ecosystems of the Gulf of Cadiz

The observed concentration of linear alkylbenzenesulfonate (LAS) in some coastal ecosystems of the Gulf of Cadiz are a function of the lack of sewage treatment plants, the water depth and the rate of renewal of the receiving water course. Concentration ranging from 2 to 510 μg.L‐1 were found in the waters of the Bay of Cadiz. Concentrations of LAS in sediments ranged from 0.4 to 49 μg g‐1. A procedure based on solid phase extraction has been developed for the isolation and concentration of LAS in environmental samples; this enables the subsequent determination of the concentrations of both total LAS and its individual homologues in marine samples with a complex organic matrix by liquid chromatography. It is a simple, sensitive and specific method.

Biodegradation kinetics of surfactants in seawater.

In this paper, a general kinetic model for degradation processes of surfactants is proposed. The model equation is v = K2S2 + K1S + K0, where v is the substrate consumption rate in the biodegradation process, S is the surfactant concentration in the medium and K2, K1, and K0 are kinetic constants. From this general expression, different simplified equations can be obtained (where K0 = 0; K2 and K0 = 0; K2 = 0; K2 and K1 = 0), which are representative of the process for different operating conditions. This model was tested by measuring the degradation of two different surfactants (Sodium dodecyl benzene sulfonate, LAS; and Sodium dodecyl sulfate, DSNa) under two different temperatures (5 and 20 degrees C). Values predicted by the model are close to experimental data obtained.

Hydrogen production from the organic fraction of municipal solid waste in anaerobic thermophilic acidogenesis: Influence of organic loading rate and microbial content of the solid waste

Hydrogen production (HP) from the organic fraction of municipal solid waste (OFMSW) under thermophilic acidogenic conditions was studied. The effect of nine different organic loading rates (OLRs) (from 9 to 220 g TVS/l/d) and hydraulic retention times (HRTs) (from 10d to 0.25 d) was investigated. Normally, butyrate was the main acid product. The biogas produced was methane- and sulfide-free at all tested OLR. Increasing the OLR resulted in an increase in both the quantity and quality of hydrogen production, except at the maximum OLR tested (220 g TVS/l/d). The maximum hydrogen content was 57% (v/v) at an OLR of 110 g TVS/l/d (HRT=0.5 d). HP was in the range of 0.1-5.7 l H2/l/d. The results have clearly shown that the increase in OLR was directly correlated with HP and microbial activity. The bacterial concentration inside the reactor is strongly influenced by the content of microorganisms in the OFMSW.

Pre-treatment optimisation studies for secondary effluent reclamation with reverse osmosis.

Physical-chemical pre-treatment was used for the reverse osmosis unit for reclamation of secondary effluents. The pilot plant was equipped with a variety of tertiary treatment units to prevent fouling and biofouling of the cellulose-acetate reverse osmosis membranes used. The optimisation of pre-treatment involved application of various concentrations of lime to raise the pH to 10.3-12.1, and to stabilise the sludge generated, as well as different dosages of ferric chloride (15, 20, and 25 mg/L) for the coagulation and solid-liquid separation. Sodium hypochlorite (8 mg/L) and UV disinfection are used for microbiological control. The water quality obtained, under the optimum conditions (pH=10.5; FeCl(3): 25 mg/L; anionic flocculant: 0.5 mg/L; sodium hypochlorite: 8 mg/L) was high, showing an average conductivity of 66 microS/cm and low COD values 4 mg O(2)/L. The product water is suitable for injection into a groundwater aquifer to counteract seawater intrusion.

Optimisation of single-phase dry-thermophilic anaerobic digestion under high organic loading rates of industrial municipal solid waste: Population dynamics

Different high feed organic loading rates (OLRs) (from 5.7 g to 46.0 g TVS/l/d) or hydraulic retention times (HRTs) (from 15 d to 2 d) in single-phase dry-thermophilic anaerobic digestion (AD) of organic fraction municipal solid waste (OFMSW) were investigated. The specific gas production (SGP) values (0.25-0.53 m(3)/kg TVS) and the percentages of Eubacteria, Archaea, H2-utilising methanogens (HUMs) and acetate-utilising methanogens (AUMs) were stable within the ranges 80.2-91.1%, 12.4-18.5%, 4.4-9.8% and 5.5-10.9%, respectively. A HUM/AUM ratio greater than 0.7 seems to be necessary to maintain very low partial pressures of H2 required for dry AD process. Increasing OLR resulted in an increase in all the populations, except for propionate-utilising acetogens (PUAs). Optimal conditions were obtained at 3d HRT (OLR=30.7 g TVS/l/d), which is lower than the doubling time of acetogens and methanogens. The methane production (MP) was clearly higher than those reported in AD of OFMSW.

Experimental evaluation of pollution potential of anionic surfactants in the marine environment

Abstract A study of the influence of temperature and salinity on the biodegradation of a commercial anionic surfactant (LAS) in waters and sediments of the Bay of Cadiz (SW Spain) is reported. The assays were carried out using batch reactors, and the surfactant concentrations used were similar to those found in the urban effluents which discharge into the bay. Temperature was found to have a decisive effect on the degradation rate. At temperatures of 20–25°C, degradation exceeded 90% within less than 10 days of assay whereas at temperatures under 10°C, degradation scarcely took place (the percentage of degradation did not exceed 5% after 21 days of assay). Variation in salinity, particularly marked during wet seasons, disturbs the activity of bacterial flora and slows down biodegradation of surfactant. All this means that the pollution potential of urban waste containing detergents undergoes significant seasonal variation. The rate of surfactant degradation was remarkably accelerated in the presence of sediments, except in those tests where anoxic conditions were established. This occurs where there is high benthic oxygen demand from sediments containing high percentage of easily-biodegradable organic matter.

Optimisation of the two-phase dry-thermophilic anaerobic digestion process of sulphate-containing municipal solid waste: Population dynamics

Microbial population dynamics and anaerobic digestion (AD) process to eight different hydraulic retention times (HRTs) (from 25d to 3.5d) in two-phase dry-thermophilic AD from sulphate-containing solid waste were investigated. Maximum values of gas production (1.9 ± 0.2 l H2/l/d; 5.4 ± 0.3 l CH4/l/d and 82 ± 9 ml H2S/l/d) and microbial activities were obtained at 4.5d HRT; where basically comprised hydrolysis step in the first phase (HRT=1.5d) and acidogenic step finished in the second phase as well as acetogenic-methanogenic steps (HRT=3d). In the first phase, hydrolytic-acidogenic bacteria (HABs) was the main group (44-77%) and Archaea, acetogens and sulphate-reducing bacteria (SRBs) contents were not significant; in the second phase (except to 2d HRT), microbial population was able to adapt to change in substrate and HRTs to ensure the proper functioning of the system and both acetogens and Archaea were dominated over SRBs. Decreasing HRT resulted in an increase in microbial activities.