Removal of pharmaceuticals from municipal wastewater by aerated submerged attached growth reactors.

The performance of four aerated submerged attached growth bioreactors was studied for the removal of three pharmaceutical micro-pollutants (fluoxetine, mefenamic acid and metoprolol) from municipal wastewater. Two packing materials (polyethylene tapes and polyurethane cubes) were compared and the effects of different organic loads (3.0, 6.0, 9.0 and 12 gCOD m-2 d-1) and of the effluent recirculation were investigated. The obtained solid retention times were in the range of 4-37 d. The reactors packed with polyurethane cubes allowed 11-26% higher biomass accumulation than the ones with polyethylene tapes and higher solid retention times. The low organic loads, high solid retention times and the implementation of effluent recirculation enhanced the removal of the three pharmaceutical compounds. The highest removals were achieved at organic load of 3 gCOD m-2 d-1 and 50% of effluent recirculation, with hydraulic residence times of 3.1-4.3 h and the solid retention times of 19-32 d. At this condition, the removals of the fluoxetine, mefenamic acid and metoprolol were up to 95, 82 and 73% respectively. The reactors with polyurethane cubes showed higher removals compared with the ones packed with polyethylene tapes.

Electrochemical removal of carbamazepine in water with Ti/PbO2 cylindrical mesh anode.

Carbamazepine (CBZ) is one of the most frequently detected organic compounds in the aquatic environment. Due to its bio-persistence and toxicity for humans and the environment its removal has become an important issue. The performance of the electrochemical oxidation process and in situ production of reactive oxygen species (ROS), such as O3 and H2O2, for CBZ removal have been studied using Ti/PbO2 cylindrical mesh anode in the presence of Na2SO4 as supporting electrolyte in a batch electrochemical reactor. In this integrated process, direct oxidation at anode and indirect oxidation by in situ electrogenerated ROS can occur simultaneously. The effect of several factors such as electrolysis time, current intensity, initial pH and oxygen flux was investigated by means of an experimental design methodology, using a 2(4) factorial matrix. CBZ removal of 83.93% was obtained and the most influential parameters turned out to be electrolysis time, current intensity and oxygen flux. Later, the optimal experimental values for CBZ degradation were obtained by means of a central composite design. The best operating conditions, analyzed by Design Expert(®) software, are the following: 110 min of electrolysis at 3.0 A, pH = 7.05 and 2.8 L O2/min. Under these optimal conditions, the model prediction (82.44%) fits very well with the experimental response (83.90 ± 0.8%). Furthermore, chemical oxygen demand decrease was quantified. Our results illustrated significant removal efficiency for the CBZ in optimized condition with second order kinetic reaction.

Wastewater treatment using a novel bioreactor with submerged packing bed of polyethylene tape.

The performance of a novel aerobic bioreactor with a specially designed submerged packing bed of high specific surface area density, made of polyethylene tape, was studied for the treatment of domestic wastewater. The reactor has a volume of 0.71 m(3) and the specific area of the packing bed was 1,098 m(2)/m(3). The operation was performed with and without effluent recycling, applying different organic loads in the range of 4.0-17.6 g COD m(-2) d(-1). No back-washings were carried out. Overall BOD(5) removals of 90-95% were obtained with organic loads of 4.0-17.6 g COD m(-2) d(-1) and HRT of 0.2-1.1 h. Overall TN removal of 69-72% was obtained at loads of 0.8-4.6 g TN m(-2) d(-1) when effluent recycling was used. The reactor allowed obtaining high quality water for urban reuse and demonstrated an effective process performance and resistance to load variations. The developed biofilm was completely penetrated by the organic matter, ammonia and oxygen, providing high removal rates. Large biomass quantities, up to 13 g dry VS/m(2), were reached in the reactor and the determined sludge yield coefficient was relatively low, of 0.25 g VSS/g COD. These results allow obtaining compact treatment systems with low sludge production and make the technology a suitable option for small wastewater treatment plants.

Treatment of petroleum production wastewater for reuse in secondary oil recovery.

Petroleum production wastewater is highly saline and contains large amounts of Ca, Mg, sulphides and hydrocarbons. The reuse of this wastewater in the secondary oil recovery can provide pollution prevention and water conservation benefits. Injection of water to the oil deposits is a frequently used method for secondary oil recovery. This operation is performed at high pressures and temperatures, because of which a suitable water quality is required to avoid deposit formation, scaling and clogging effects. The objective of this study was to select the best treatment system for the oil production wastewater, generated in one of the Mexican oil extraction facilities, for the implementation of this kind of reuse by injecting the treated water to sand formations with 12-15% porosity. A complete characterization of the petroleum production wastewater was done. Based on laboratory tests, three basic treatment options were suggested and evaluated in a pilot plant. The most suitable treatment was determined by injecting the different treated waters in samples of the real formations. The selected system consists in softening, followed by oxidation, decarbonation and filtration. This train allowed 99.8% hardness removal, a complete S(2-) removal, as well as 99% TSS, 78% TOC, 98% Sr, 86% Ba, 51% Si and 17% Fe removals.

Treatment of organic synthesis wastewater using anaerobic packed bed and aerobic suspended growth bioreactors.

The performance of an anaerobic mesophilic packed bed reactor, with a mixture of GAC and tezontle, followed by an aerobic suspended growth system was studied for the treatment of organic chemical wastewater with a high COD concentration (22-29 g/L). The testing of the anaerobic-aerobic system was conducted in an experimental set-up for almost 2.5 years. Different operational conditions were evaluated. The anaerobic reactor showed performance stability and COD removals higher than 80% were obtained with loads up to 16.6 kg x m(-3) x d(-1). The acclimation of the aerobic biomass to the substrate in the anaerobic effluent was very quick and COD removals higher than 94% were obtained even at high organic loads. The combined anaerobic-aerobic system allowed total COD removals higher than 99.5% and the accomplishment of the discharge requirements of 200 mgCOD/L when the anaerobic reactor was operated with loads of 8-11 kg x m(-3)x d(-1) and the aerobic reactor with 0.33 kg x kg(-1) x d(-1), being the total HRT of 4.4. The average TKN removal in the anaerobic-aerobic system was 97%, the average for the anaerobic reactor being 52% and that one for the aerobic system being 94%.

Anaerobic treatment of organic chemical wastewater using packed bed reactors.

The studied organic chemical wastewater had a high COD, 20-45g/L, and low TSS, less than 200 mg/L, making anaerobic bio-filtration a suitable treatment method. The organic matter consisted of alcohols, amines, ketones and aromatic compounds, such as toluene and phenol. Granulated activated carbon (GAC) and a porous stone called tezontle, widely available in Mexico, were used as a bio-film support. Once inoculated, the mesophilic reactors with granulated activated carbon (GAC-BFs) reached stability with 80% COD removal in 40 days, while the reactors with tezontle material (tezontle-BF) required 145 days. Biodegradation of more than 95% was obtained with both support media: at organic loads less than 1.7 kg m(-3) d (-1) in tezontle-BF and with loads of up to 13.3 kg m(-3) d(-1) in GAC-BFs. The bio-filters with GAC allowed COD removal efficiency of 80% at a load as high as 26.3 kg m (-3) d(-1), while the same efficiency with tezontle was obtained at loads up to 4.45 kgm (-3d) (-1). The use of GAC as support material allows greater biodegradation rates than tezontle and it makes the bio-filters more resistant to organic increases, inhibition effects and toxicity. Methanogenic activity was inhibited at loads higher than 1.7 kg m(-3) d(-1) in bio-filters with tezontle and 22.8 kg m(-3) d(-1 ) in bio-filters with GAC. At loads lower than the previously mentioned, high methane production yield was obtained, 0.32-0.35 m(3) CH4/kg COD removed. The biomass growth rates were low in the bio-filters with both kinds of material; however, a sufficiently high biomass holdup was obtained.

Anaerobic biodegradation of chlorinated aliphatic compounds using packed bed reactors.

The feasibility of anaerobic packed bed reactors with tezontle (volcanic stone widely available in Mexico) and mineral granular activated carbon (GAC) was explored for the degradation of the main chlorinated aliphatic compounds present in the effluent from chemical industry for ethylene and polyvinyl chloride production. The biofilm on the support materials was developed using as inoculums anaerobic sludge. The biodegradation of the halogenated aliphatic compounds (1,2-dichloroethane; 1, 1, 1 -trichloroethane; trichloroethylene and carbon tetrachloride) was possible without addition of external electron donors. High COD removal was obtained in the reactors with both materials. The use of GAC as a biomass support allows a complete biodegradation of the chlorinated aliphatic compounds at organic loads up to 1.24 kgCOD.m(-3).d(-1), with 94% of COD removal and with a biodegradation rate of 2.062 gCOD.kgGAC(-1).d(-1). The reactor with tezontle also had high biodegradation capacity, but the biodegradation of the 1, 1 -dichloroethene, which appeared as intermediate product, was not reached at the required level in the studied range of organic loads.

Treatment techniques for the recycling of bottle washing water in the soft drinks industry.

The soft drink production is an important sector in the manufacturing industry of Mexico. Water is the main source in the production of soft drinks. Wastewater from bottle washing is almost 50% of the total wastewater generated by this industry. In order to reduce the consumption of water, the water of the last bottle rinse can be reused in to the bottle pre-rinse and pre-washing cycles. This work presents the characterization of the final bottle washing rinse discharge and the treatability study for the most appropriate treatment system for recycling. Average characteristics of the final bottle wash rinse were as follows: Turbidity 40.46 NTU, COD 47.7 mg/L, TSS 56 mg/L, TS 693.6 mg/L, electrical conductivity 1,194 microS/cm. The results of the treatability tests showed that the final rinse water can be used in the pre-rinse and pre-washing after removing the totality of the suspended solids, 80% of the COD and 75% of the dissolved solids. This can be done using the following treatment systems: filtration-adsorption-reverse osmosis, or filtration-adsorption-ion exchange. The installation of these treatment techniques in the soft drink industry would decrease bottle washing water consumption by 50%.

Characterization and dewaterability of raw and stabilized sludge using different treatment methods.

A comparison of the characteristics and stabilization potential of the four most used sludge treatment systems in Mexico was made. A pilot plant constituted by separate systems for anaerobic and aerobic digestion, lime stabilization, conditioning and dewatering, was built and operated during four months in one of the biological wastewater treatment plants in Acapulco, Mexico. Composting of sludge was also made. An aerobic static pile was built using bulking materials available in the region. A turbine centrifuge was used for dewatering the stabilized sludge and results showed good performance of the device. The main problem for the beneficial use of treated sludge was its pathogenicity. The composting process allowed us to obtain a product with approximately 20 fecal coliform density (MPN/g); with lime stabilization, the sludge produced had a fecal coliform density of 2 MPN/g. From these results, it is concluded that both the composting process and the alkaline stabilization with lime produce a well stabilized sludge, bacteriologically safe that accomplishes the requirements for its use on soil without restrictions. Related to parasitological removal, the best helminth egg removals were obtained also using these two processes. Ascaris sp. densities in raw sludge (309-430 eggs/g) were reduced to a final density of 3-14 eggs/g in the aerobic composting process and to 4-18 eggs/g in the lime stabilized sludge. Removal is not high enough to reach the recommended level for unrestricted use of stabilized sludge.