Predicting impacts of water conservation with a stochastic sewer model

Abstract

Population growth and climate change put a strain on water resources; hence, there are growing initiatives to reduce water use. Reducing household water use will likely reduce sewer input. This work demonstrates the use of a stochastic sewer model to quantify the effect water conservation has on sewer hydraulics and wastewater concentration. Probabilistic discharge patterns have been developed using SIMDEUM WW® and fed into hydraulic modelling software InfoWorks ICM® to produce likely flow and quality profiles for five future water use scenarios. The scenarios tested were developed to outline how commercial and political factors may change water use in future. Scenario testing revealed that 15–60% water reduction reflected a 1–48% drop in the morning peak flow. The water use reduction was predicted to increase wastewater concentrations of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN) and total phosphorus (TPH) by 55–180%, 19–116% and 30–206% respectively. The sewer flow model was developed, calibrated and validated using a case study in the Wessex Water region of the UK and all future scenarios were compared to the validated baseline case. This wastewater flow and quality model allows scenario testing, which could help redesign future sewer networks to better prepare for water conservation strategies.

A Stochastic Model to Predict Flow, Nutrient and Temperature Changes in a Sewer under Water Conservation Scenarios

“…This model has been demonstrated as a useful tool for analysis of various resource recovery options for future urban water planning. Bailey et al [13] concluded that this model over-predicts phosphorus concentrations, but with the results from the sampling campaign, and the changes made in the estimated wastewater composition due to the removal of phosphorus in detergents (Section 2.1.2), the model now predicts in line with reality. Daily pollutant load produced per capita in these scenarios ranged from 86-122 g COD, 8-12 g TKN and 0.8-1.2 g TPH-these values align with independently published values [21,[28][29][30].…”

“…Therefore, a review of relevant literature [5,[15][16][17][18][19] was conducted to find appropriate input values for nutrient simulation. These input parameters describe pollutant mass per discharge for each household appliance (see Table 1), and the derivation of these parameters is described in Bailey et al [13]. The nutrient discharge aspect of SIMDEUM WW ® has never been validated.…”

“…Table 1. Appliance-specific pollutant concentrations for improved SIMDEUM WW ® (adapted from Bailey et al [13]). Bold values were defined in this work using observed wastewater data.…”

“…Saint-Venant equations govern hydraulics in InfoWorks ® ICM. The wastewater quality model runs parallel to the hydraulic model, as described in Bailey et al [13], but was not validated. The concentration of dissolved pollutants and suspended sediment at every node in the sewer network is calculated for every time step using the InfoWorks ® Network Model.…”

“…The flow model was validated using data from an English catchment, provided by Wessex Water (UK-based water utility). The flow model was extended to include wastewater pollutant concentrations by linking typical wastewater quality data to appliance-specific discharges within SIMDEUM WW ® and utilising the InfoWorks ® ICM wastewater quality model [13]. The flow/quality model was used to simulate and compare a series of future water use scenarios.…”