By Dr Karen Scott (@DrKarenScott)
|One of the streets during the Hull 2007 floods.|
Gully pots are small sumps in the roadside gutter and are important components of the urban drainage system with over 17 million in use across England and Wales, approximately 73,000 of these in Hull. Their main purpose is to collect sediment from road runoff, organic matter and litter before it enters the drainage system where potential blockages could occur. Due to the large amount of materials they collect they require regular cleaning to prevent the pots themselves becoming blocked.
|A. Diagram of a large square gully pot. B. Inside the gully pot showing waste collected within.|
This introductory section of my research aimed to create an initial understanding of the physical and microbial processes within the gully pot waste, the ability of it to decompose, and whether season and geographical locations affected it. To assess this, two lots of experiments were set up - in the field and in the laboratory. In the field, the city of Hull was divided into four main areas – industrial, residential, busy road and areas with high foliage. Gully pots from these four areas were randomly sampled on a monthly basis over a year (which allowed for seasonal differences to be monitored).
|Modelled laboratory composting experiment|
The finding from the one year field study showed that area had more of an impact than season. Differences in organic matter was observed in the seasons where it was higher in summer (potentially due to high land use e.g gardening which would decrease when the weather got worse and leaf fall during the late summer months) and lower pH in autumn and winter. These differences did not appear to affect the enzyme activity, where similar activity was observed across the seasons. Looking across the geographical area types, organic matter was considerably lower in industrial areas (due to the lack of vegetation) and pH was higher (potentially due the dumping of industrial detritus, such as cement, which was observed in samples). Enzyme activity was higher in samples with higher organic matter values, it was also present in the samples with less organic matter, but just at lower levels. The results from the five week trial showed that the contents from the gully pots are able to decompose in modelled laboratory environments. Organic content decreased at an average rate of 0.1g of organic matter per 13g of organic matter per day. Although the rate of decomposition was observed to be slow it quantifies a previously unknown degradation process.
While significant differences in the parameters monitored between gully pots were recorded, it was difficult to show any distinct nature of the different gully pot contents. Therefore, it may be possible to treat gully waste in a homogenous manner, rather than individually, especially in a seasonal context. This may greatly assist future research to determine the activity of the contents via replica systems in a laboratory or otherwise, and can be used as a baseline when examining sustainable solutions for urban drainage waste
Scott et al., 2012. An initial appraisal of waste decomposition by microbial processes within roadside gully pots. Waste Management and Research. 31(8).
This paper can be found here.