Developing cold-adapted biomass for the anaerobic treatment of domestic wastewater at low temperatures (4, 8 and 15 °C) with inocula from cold environments.

Temperature is the bottleneck for the anaerobic treatment of domestic wastewater in temperate climates. Most previous attempts to achieve anaerobic treatment at low temperatures have attempted to acclimatize mesophilic sludge and have failed at temperatures below 10-13 °C. We describe an alternative approach using communities from environments that have been exposed to low temperatures over evolutionary time-scales as seed for such reactors. Batch reactors were inoculated with a mixture of soils and sediments from the high Arctic and an Alpine lake to treat UV-sterilized raw domestic wastewater at 4, 8 and 15 °C. To evaluate the intrinsic treatment capacity of the bacteria the specific rates of methanogenesis and hydrolysis were evaluated. Specific methanogenic activity at 4, 8 and 15 °C was 6.3, 7.6 and 10.3 fmol CH4 cell-1day-1 respectively. Specific putative hydrolysis rates were 76.2, 186.6 and 251.9 fgrams COD cell-1day-1. Hydrolysis was twice as temperature sensitive as methanogenesis (Q10: 4.62 and 1.57 respectively). The specific rates are over ten times higher than we have previously observed in microcosms fed with settled wastewater at the same temperatures. The results imply that inoculating reactors with cold-adapted communities is a promising way to develop biomass capable of treating anaerobic wastewater treatment at low temperatures whilst achieving an effluent that conforms to the EC Directive COD standards. Large-scale reactors are feasible if satisfactory cell concentrations can be achieved.

Low-temperature limitation of bioreactor sludge in anaerobic treatment of domestic wastewater.

Two strategies exist for seeding low-temperature anaerobic reactors: the use of specialist psychrophilic biomass or mesophilic bioreactor sludge acclimated to low temperature. We sought to determine the low-temperature limitation of anaerobic sludge from a bioreactor acclimated to UK temperatures (<15 °C). Anaerobic incubation tests using low-strength real domestic wastewater (DWW) and various alternative soluble COD sources were conducted at 4, 8 and 15 °C; methanogenesis and acidogenesis were monitored separately. Production of methane and acetate was observed; decreasing temperature resulted in decreased yields and increased 'start-up' times. At 4 °C methanogenesis not hydrolysis/acidogenesis was rate-limiting. The final methane yields at 4 °C were less than 35% of the theoretical potential whilst at 8 and 15 °C more than 75 and 100% of the theoretical yield was achieved respectively. We propose that the lower temperature limit for DWW treatment with anaerobic bioreactor sludge lies between 8 and 4 °C and that 8 °C is the threshold for reliable operation.

Seasonal variations in antibiotic resistance gene transport in the almendares river, havana, cuba.

Numerous studies have quantified antibiotic resistance genes (ARG) in rivers and streams around the world, and significant relationships have been shown that relate different pollutant outputs and increased local ARG levels. However, most studies have not considered ambient flow conditions, which can vary dramatically especially in tropical countries. Here, ARG were quantified in water column and sediment samples during the dry- and wet-seasons to assess how seasonal and other factors influence ARG transport down the Almendares River (Havana, Cuba). Eight locations were sampled and stream flow estimated during both seasons; qPCR was used to quantify four tetracycline, two erythromycin, and three beta-lactam resistance genes. ARG concentrations were higher in wet-season versus dry-season samples, which combined with higher flows, indicated much greater ARG transport downstream during the wet-season. However, water column ARG levels were more spatially variable in the dry-season than the wet-season, with the proximity of waste outfalls strongly influencing local ARG levels. Results confirm that dry-season sampling provides a useful picture of the impact of individual waste inputs on local stream ARG levels, whereas the majority of ARGs in this tropical river were transported downstream during the wet-season, possibly due to re-entrainment of ARG from sediments.

Antibiotic resistance gene abundances associated with waste discharges to the Almendares River near Havana, Cuba.

Considerable debate exists over the primary cause of increased antibiotic resistance (AR) worldwide. Evidence suggests increasing AR results from overuse of antibiotics in medicine and therapeutic and nontherapeutic applications in agriculture. However, pollution also can influence environmental AR, particularly associated with heavy metal, pharmaceutical, and other waste releases, although the relative scale of the "pollution" contribution is poorly defined, which restricts targeted mitigation efforts. The question is "where to study and quantify AR from pollution versus other causes to best understand the pollution effect". One useful site is Cuba because industrial pollution broadly exists; antibiotics are used sparingly in medicine and agriculture; and multiresistant bacterial infections are increasing in clinical settings without explanation. Within this context, we quantified 13 antibiotic resistance genes (ARG; indicators of AR potential), 6 heavy metals, 3 antibiotics, and 17 other organic pollutants at 8 locations along the Almendares River in western Havana at sites bracketing known waste discharge points, including a large solid waste landfill and various pharmaceutical factories. Significant correlations (p < 0.05) were found between sediment ARG levels, especially for tetracyclines and ß-lactams (e.g., tet(M), tet(O), tet(Q), tet(W), bla(OXA)), and sediment Cu and water column ampicillin levels in the river. Further, sediment ARG levels increased by up to 3 orders of magnitude downstream of the pharmaceutical factories and were highest where human population densities also were high. Although explicit links are not shown, results suggest that pollution has increased background AR levels in a setting where other causes of AR are less prevalent.