Effectiveness of the use of Ag, Cu and PAA to disinfect municipal wastewater.

The WHO defines Category A wastewater as one which does not contain more than 1000 FCU 100 ml(-1) of faecal coliforms (FC) and less than 1 helminth egg (HE) per litre. The objectives of this work were to determine: 1) the disinfectant capacity of different concentrations of silver (Ag), silver-copper (Ag-Cu) and silver-copper-peracetic acid (Ag-Cu-PAA) when added to samples of raw wastewater (RW), with a contact time of 60 minutes; 2) the optimal concentration and contact time required by the better performing disinfectant, determined from the previous stage, to obtain Category A RW; 3) the effect of the selected disinfectant when applied to RW, the effluent of activated sludge (ASE) and the effluent of sand filters (FE) for 10, 30 and 60 min duration. The Ag:Cu:PAA ratio of 0.6:6.0:100.0 mg l(-1), showed the best disinfectant capability to produce Category A wastewater. The ratio of 0.1:1.0:20.0 mg l(-1) of Ag:Cu:PAA and a contact time of 10 minutes are the optimal values to produce Category A wastewater in RW. For RW and ASE, the optimal ratios and times for Ag:Cu:PAA were: 1.2:12.0:90.0 mg l(-1) at 60 min and 0.1:1.0:20.0 for 10 min, respectively. The FE samples showed concentrations of FC and HE below the standards of the WHO; therefore, their disinfection is not necessary.

Adding silver and copper to hydrogen peroxide and peracetic acid in the disinfection of an advanced primary treatment effluent.

This paper evaluates the efficacy of hydrogen peroxide (HP) and peracetic acid (PAA) in the disinfection of an Advanced Primary Treatment (APT) effluent, and how said disinfection capacities can be enhanced by combining the oxidants with copper (Cu2+) and silver (Ag). The treatment sequence consisted of APT (adding chemicals to water to remove suspended solids by coagulation and flocculation), followed by disinfection with various doses of HP, HP+Cu2+, HP+Ag, PAA and PAA+Ag. Microbiological quality was determined by monitoring concentrations of fecal coliforms (FC), pathogenic bacteria (PB) and helminth eggs (HE) throughout the sequence. The results revealed that APT effluent still contains very high levels of bacteria as the treatment only removes 1-2 log of FC and PB, but the reduction in the number of viable helminth eggs was 83%. Subsequent disinfection stages demonstrated that both HP+Cu2+ and HP+Ag have a marked disinfection capacity for bacteria (3.9 and 3.4 log-inactivation, respectively). Peracetic acid on its own was already extremely efficient at disinfecting for bacteria, and the effect was enhanced when combining PAA with silver (PAA+Ag). The best result for HE removal was achieved by combining PAA with silver (PAA+Ag) at doses of 20 + 2.0 mg l(-1), respectively. The study concluded that the PAA+Ag and HP+Ag combinations were good alternatives for APT effluent disinfection, because the disinfected effluents met the standards in NOM-001-SEMARNAT-1996, Mexico's regulation governing the microbiological quality required in treated wastewater destined for unrestricted reuse in agricultural irrigation (< or =1 helminths per litre). Combining either of these disinfection treatments with a primary method such as APT, therefore, offers an effective and practical way of reducing the health risks normally associated with the reuse of wastewaters.

Ciliatological characterization of a biological reactor that eliminates nitrogen with intermitent aeration

El presente trabajo tiene por objetivo la determinación de los ciliados presentes en un reactor biológico con alternancia de aireación empleado para la eliminación de compuestos nitrogenados. El sistema de tratamiento usado fue de tipo lodos activados, con un volumen de trabajo de 30 litros, tiempo de residencia hidraúlico de 20 horas y tiempo de retención celular de 15 días. El reactor operó a 15 ºC y fue alimentado con agua residual doméstica, proporcionandole de manera alternada una hora de aireación por cada hora de no aireación, incorporándole de manera periódica acetato de sodio para favorecer la fase de desnitrificación. En términos globales el reactor logró una eliminación del 95 por ciento del material orgánico disuelto. Durante la fase de operación pseudoestable se presentaron 16 especies de ciliados (Phyllum Ciliophora), las cuales están distribuídas en 13 géneros; 12 familias; 7 órdenes; 6 subclases; 5 clases y 3 subphyla. De ellas 9 son libres nadadoras y 7 son sésiles. El subphyllum con mayor riqueza de especies fue el Cyrtophora, siendo la clase Oligohymenophorea la mejor representada y correspondiendo a la subclase Peritricha el mayor número de especies. Casi la totalidad de los ciliados encontrados has sido reportados como habitantes comunes en plantas de tratamiento de lodos activados convencionales con altas eficiencias depurativas y han sido catalogados dentro del sistema de ciliados saprobios, ubicándose principalmente en los niveles alfa y ß mesosaprobios. La presencia de esta comunidad de ciliados concuerda tanto con el nivel de eliminación de contaminantes carbonados, como nitrogenados. En consecuencia puede inferirse la factibilidad de evaluar la calidad operativa de un reactor aerobio/anóxico, a partir de la observación directa de la comunidad de ciliados prevaleciente

Ciliatological characterization of a biological reactor that eliminates nitrogen with intermitent aeration.

Ciliates present in an activated sludge biological reactor used for removal of nitrogen compounds with intermitent aeration were determined. The reactor had a working volume of 30 liters, a hydraulic residence time of 20 hours, and a cell retention time of 15 days. Operating temperature was 15 degrees C, and it was fed with domestic sewage. Aeration was given in pulses, one hour aeration and one hour without aeration, feeding sodium acetate to favour denitrification processes. Elimination efficiency was 95% of the dissolved organic matter. During the pseudostable operating phase, 16 species of ciliates (Phylum Ciliophora) were found. They were distributed as follows: 13 Genera; 12 Families; 7 Orders; 6 Subclasses; 5 Classes, and 3 Subphyla. From them, 9 are free swimmers and 7 are pedunculates. The Subphylum with higher diversity of species was the Ciliophora. The Oligohymenophorea Class was the best represented, corresponding to the Peritricha Subclass the highest number of species. Almost all the ciliates found have been reported as common inhabitants of activated sludge wastewater treatment plants with high removal efficiencies. They are catalogued as saprobe ciliates, within a and b masosaprobe levels. The presence of this ciliate community agrees with the carbon and nitrogen compounds removal efficiencies. Consequently, there exists the possibility of evaluating the operational efficiency of an aerobic/anoxic reactor using direct ciliates observations.

[Comparison of ciliate diversity in biodisc reactors which purify industrial wastewater]. / Comparación de la diversidad de ciliados en reactores de biodiscos que depuran aguas residuales industriales.

The comparative study of the ciliate populations present in rotating biological reactors (biodiscs reactors) of 20 l working volume, treating three different wastewaters is the aim of this project. Wastewaters chosen were those of a maize mill, of a sugarcane/ethyl alcohol plant, and of a recycled paper mill. Its dissolved organic contents, measured as soluble chemical oxygen demand (COD) and five-day biochemical oxygen demand (BOD5), were 2040 mg COD/l and 585 mg BOD5/l for maize mill effluents (nejayote), 2000 mg COD/l and 640 mg BOD5/l for sugarcane/ethanol effluents (vinasses), and 960 mg COD/l and 120 mg BOD5/l for whitewaters of the paper industry. Results obtained indicate that ciliate proliferate in all chambers of reactors treating these wastewaters. The ciliates were more abundant in vinasses, followed by nejayote, and then whitewaters. Among protozoa, ciliates were present as follows: 19 species in total. Three of them were common for the three systems. Free swimming ciliates were in higher proportion than pedunculated ones. Its diversity was higher for the whitewaters system, next for nejayote, and the lesser, for vinasses, corroborating the fact that less polluted waters have higher organisms' diversity.