Microbiological characteristics in urban stormwater runoff and sediments

This study was undertaken to investigate the microbiological composition of urban surface water runoff and sediments in both North London and Valencia. The survey focused primarily on the relationships between indicator microorganisms (total coliforms, faecal coliforms and faecal streptococci) and water quality, and between indicator microorganisms and pathogens (Pseudomonas aeruginosa and Salmonella) which cause waterborne disease.
High levels of microorganisms were found in dry weather flow sanitary wastewater, combined sewage, urban receiving stream, beach outfall and storm water runoff as well as sediments. Pathogenic bacteria were consistently isolated from the urban water courses. Pseudomonas aeruginosa were recovered at high concentration and Salmonella
required concentration for enumeration.
The results indicated that storm water runoff from urban areas contain high levels of indicator microorganisms and pathogenic bacteria. The pollution appears to be predominantly of non-human origin and is mainly derived from animal wastes. In general, the runoff resembled dilute raw sewage in microbiological composition and obversely represents a public health risk.
Although some connection between bacteria densities and selected environmental factors is apparent, the relationship is not simple. Factors such as BOD₅, flow, temperature, pH, faecal deposit age and hydrologic proximity of pollution sources all affect bacterial densities in runoff and according to different water sources. However, the parameter of bacterial loading may be used in survey of aquatic environment to estimate probable bacteria density ranges.
The characteristics of bacterial concentration in different layers of sediments and bacterial release from sediment in a continuous flow tank have also been investigated. Indicator and pathogenic bacteria occur at the highest concentration in the upper layers of sediment. Pseudomonas aeruginosa was more easy released than indicator microorganisms. The microbial release peak was detected at 6 hours. The ratio of faecal coliform to faecal streptococcus densities can be used to help identify particular sources of faecal pollution and had relatively small fluctuation rate after faeces deposited in water under 4°C than 20°C.