Sergio Papiri

First flush in a combined sewer system

Pollutant first flush was examined in an urban catchment with area of 12.7 ha and drained by a combined sewer system located in northern Italy. A total of 23 rainfall-runoff events were monitored and 281 samples were analyzed. The selected quality parameters were biochemical oxygen demand, chemical oxygen demand, suspended solids, settleable solids, total phosphorus, total nitrogen, ammonium nitrogen, lead, and zinc, specific conductivity and hydrocarbons. A subset of representative storms was selected for first flush analysis. The catchment presented a strong first flush for almost all storms and most constituents. The analysis shows that treating the maximum amount of the early part of the runoff is a better strategy than treating a constant flow rate. Best management practices that can treat or store the first runoff are favored in this kind of system for these water quality parameters.

Simplified Procedure for Water Distribution Networks Reliability Assessment

This work describes a simple procedure for the analysis of water distribution system (WDS) performance. It is based on the reliability assessment of a WDS during failure states resulting from the unavailability of a pipe (maintenance or repair), taking into account the probability of the failure events. The procedure may consider changes in daily demand by using patterns defined to represent seasonal trends. Applying this method to a network with around 200 pipes demonstrates its usefulness, especially when the aim is to objectively compare different design solutions. The procedure takes also into account variations in design parameters such as an increase in water demand and/or a drop in hydraulic conductance resulting from pipe lining degradations (corrosion or deposits). DOI: 10.1061/(ASCE)WR.1943- 5452.0000184.

Procedure for Defining a Pressure-Outflow Relationship Regarding Indoor Demands in Pressure-Driven Analysis of Water Distribution Networks

The definition of the relationship between the actual flow delivered by a node of a water distribution network and the available nodal pressure head is one of most crucial problems in Pressure Driven Analysis (PDA). The paper proposes a procedure, based on two models (building model and supplied urban area model), by means of which it is possible to generate and to simulate numerous different scenarios regarding the water delivery in the urban area supplied by a distribution network node. The scenarios are achieved by reproducing, through appropriate random generators, several urban and hydraulic situations, which are defined by various parameters governing water delivery. The statistical processing of the simulation results allows to define a representative pressure-flow relationship which reproduces, on average, the complex and varied set of phenomena governing the actual water delivery. Two application examples are also presented; the results of these study cases allow to calibrate the Tanyimboh and Templeman (2010) relationship, which is good for incorporation in PDA algorithms, because it is continuous with its first order derivatives in the whole field of pressure head values.

Impact assessment of urban wet-weather sewer discharges on the Vernavola river (Northern Italy)

The research concerned the ecological impact assessment of urban wet-weather sewer discharges on the Vernavola river (Pavia, Northern Italy) focusing both on the sewer system and on the receiving natural environment. The complexity of the urban drainage system (combined sewer networks, pumping stations, stormwater storage tanks, etc.) was characterised through in situ inspections, measurements and numerical modelling. Various dry- and wet-weather monitoring campaigns on the Vernavola river provided the water quality tracers according to Italian standards: dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, ammonium, nitrate and Escherichia coli. The quality analyses were also devoted to the study of the macro-benthic community. Both the chemical and biological river quality appeared significantly affected by sewer overflow contaminants. During storm events the receiver ecosystem was severely loaded with organic pollution (wet-weather discharges were equivalent to a civil sewer discharge of about 68,000 population equivalent (PE)) and the biodiversity of the benthonic organisms populating the stream was reduced by the physical modification of the habitat. These sampling and modelling studies provided the priority support information for promoting solutions and management strategies on the entire chain ‘sewer system-treatment plant-receiving natural environment’ necessary to reach the stream quality objectives.

Placement Strategies and Cumulative Effects of Wet-weather Control Practices for Intermunicipal Sewerage Systems

This study investigates the rainfall-runoff process and the pollutant dynamics on theoretical catchments and intermunicipal sewer systems in order to characterize the hydraulic and environmental performance of possible types of sewerage system and to compare the effectiveness of different wet-weather control schemes for intermunicipal sewerage systems. A comprehensive investigation on the placement strategies and the cumulative effects of wet-weather control practices is carried out over a broad watershed as a key preliminary step in addressing surface water safeguard requirements in developing and urban areas. The analysis shows that the different types of intermunicipal sewer system exhibit slightly different performance. Placing wet-weather detention tanks at different spatial levels affects the overall effectiveness of the wet-weather control system. In the examined case study schemes, the insertion of a wet-weather detention tank is better on final than on local flow regulators. The performance control also proves to be easier adopting the solution with intermunicipal tank since, for this scheme, the design criteria have a more important influence than rainfall characteristics on the environmental performance. These results represent an issue of primary focus for the implementation of environmental policies and mitigation strategies against surface water impairment in urban and developing areas.