Water pollution news: Wastewater and Antibiotic Resistance.

Article4: Chemistry Views

Bacterial Resistance in Wastewater

Bacterial resistance to antibiotics is a growing concern. Even low environmental levels of antibiotics can result in increased bacterial resistance at specific locations. Recently, there have been reports of high levels of several broad spectrum fluoroquinolone antibiotics in effluent and surface water from an Indian wastewater treatment plant.

Joakim Larsson and colleagues, University of Gothenburg, Sweden, have used culture-independent shotgun metagenomics to investigate microbial communities in these river sediments. River sediment samples were collected up- and downstream from an Indian waste water treatment plant.

High-throughput sequencing of DNA in the samples showed bacterial diversity downstream was slightly lower than upstream, and very high levels of resistance genes were identified. Elements for horizontal gene transfer, including integrons, transposons and plasmids were also detected. These help spread resistance between bacterial species including to human pathogens.

Article 5 : Chemical & Engineering News

Spreading antibiotic resistance in wastewater treatment

When people pop antibiotics to treat infections, the drugs often end up excreted into sewage. As scientists continue to find these antibiotics in the wastewater coming from homes and hospitals, they worry that the drugs’ presence is fueling the spread of antibiotic resistance. At the American Chemical Society meeting in Anaheim, Calif., researchers reported that wastewater contains other chemicals that might also promote antibiotic resistance: heavy metals.

Environmental scientists have previously observed a connection between metals and antibiotic resistance in metal-contaminated soils and freshwater sediments. The bacteria living in these environments had significantly higher levels of resistance than bacteria from noncontaminated soils.

Edward F. Peltier of the University of Kansas, Lawrence; David Graham of Newcastle University, in England; and their colleagues wondered if the phenomenon also occurred in wastewater treatment plants. These plants are a unique environment where, along with antibiotics, metals such as zinc and copper are common. Bacteria also play a key role in the treatment process. After removing solids from wastewater, treatment plants mix it with a sludge containing an array of bacteria that chew up dissolved organic compounds.

…They found that copper alone, in the absence of antibiotics, could promote resistance to the antibiotic ciprofloxacin, with resistance levels jumping from a baseline level of 7% of the reactor population after the first phase to 11% after the second phase. Zinc alone didn’t have an effect, but in the presence of certain antibiotics it did enhance resistance levels. In reactors receiving zinc and tetracycline, 63% of the bacteria were resistant to the antibiotic. Meanwhile, resistance levels in reactors that received tetracycline and no metal were only 44%.

If metals do help spread antibiotic resistance in wastewater treatment plants, then they could be a more long-lasting source of resistance than are antibiotics themselves, Peltier says. “Antibiotics can degrade, metals can’t,” he says…

A wastewater treatment plant at the top of this article was shot by Kristian Bjornard, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license This article was Posted by Brian Thomas at 7:23 PM /Monday, March 28, 2011

The following article is a comparison of aerobic and anaerobic digestion. In both aerobic and anaerobic systems the growing and reproducing microorganisms within them require a source of elemental oxygen to survive.^[1]

In an anaerobic system there is an absence of gaseous oxygen. In an anaerobic digester, gaseous oxygen is prevented from entering the system through physical containment in sealed tanks. Anaerobes access oxygen from sources other than the surrounding air. The oxygen source for these microorganisms can be the organic material itself or alternatively may be supplied by inorganic oxides from within the input material. When the oxygen source in an anaerobic system is derived from the organic material itself, then the ‘intermediate’ end products are primarily alcohols, aldehydes, and organic acids plus carbon dioxide. In the presence of specialised methanogens, the intermediates are converted to the ‘final’ end products of methane, carbon dioxide with trace levels of hydrogen sulfide.^[2] In an anaerobic system the majority of the chemical energy contained within the starting material is released by methanogenic bacteria as methane.^[3]

In an aerobic system, such as composting, the microorganisms access free, gaseous oxygen directly from the surrounding atmosphere. The end products of an aerobic process are primarily carbon dioxide and water which are the stable, oxidised forms of carbon and hydrogen. If the biodegradable starting material contains nitrogen, phosphorus and sulfur, then the end products may also include their oxidised forms- nitrate, phosphate and sulfate.^[1] In an aerobic system the majority of the energy in the starting material is released as heat by their oxidisation into carbon dioxide and water.^[3]

Composting systems typically include organisms such as fungi that are able to break down lignin and celluloses to a greater extent than anaerobic bacteria.^[4] Due to this fact it is possible, following anaerobic digestion, to compost the anaerobic digestate allowing further volume reduction and stabilisation.^[5]

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