Development of a low-cost sewer sampling system

Cassandra Trent (Watercare Services Limited, Remuera Road, Newmarket), 

Brent Gilpin (Institute of Environmental Science and Research) 

Rosemary Sim (Watercare Laboratory Services)

Sewer sampling is useful for monitoring a range of environmental parameters,
trade waste parameters and indicators of public health such as the prevalence of
SARS-CoV-2 genetic material. To obtain indicative samples of the sewage from a
defined catchment, composite samples are optimal as they provide multiple snap
shots of the sewage at different time points. Composite sampling currently
requires the use of a large auto-sampling device. This device needs to be
installed in a safe, secure, and accessible site. When monitoring specific sewage
catchments, finding a suitable site for an autosampler can be challenging. While
pump stations are safe and secure, they are not always in the best location for a
desired catchment. Manholes across the network are predominantly the best
way to divide a catchment for sampling purposes. However, modern manholes
are increasingly installed with safety grates to minimize the risk of falls into the
sewer of the public and staff. There are currently no composite auto-samplers on
the market that can be fitted to the safety grates in these manholes.
To overcome these challenges, a low-cost sewer sampling system was designed
able to be deployed into a manhole fitted with a safety grate. The device is
intrinsically safe, uses low-cost materials and is reusable. A composite can be
generated of up to 1.5L of sample. Additional benefits include less need for a
series of grab samples, samples that are more representative, ability to deploy
anywhere across the network and the possibility of use in remote locations such
as dams, other suitable freshwater locations and sites without power.
The prototype sampler was deployed in stagnant and flowing water in March
2021 with great success and was originally developed to assist capturing SARS-CoV-2 genetic material in specific catchments. Sewer trials are planned for late March/April to prepare for same day setup of sampling sites in locations of
interest across the network if community transmission is suspected. This may also be a suitable low-cost option for a range of alternate applications especially where an intrinsically safe device is required.