Project: Optimization and Upgrading of wastewater treatment plant in San Giovanni Lupatoto
Location: Province of Verona, Italy
Client: Acque Veronesi S.c.a.r.l.
Cost of total Works: €4,050,500
Services: Preliminary design, Final design, S.I.A.
The town where the wastewater treatment plant in question is located is San Giovanni Lupatoto, a small town close to the city of Verona which in the last fifteen years has undergone a considerable increase in population. The existing wastewater treatment plant was designed in the early 1980’s for 24,000 E.P. and to respect the limit of pollutants of the earlier legislation. In the last ten years some important new laws have been passed regarding pollutants in rivers and the restrictions on the pollutants allowed in wastewater discharged into rivers.
The optimization and the upgrading of the existing wastewater plant thus became a priority for the town of San Giovanni Lupatoto.
The interventions were designed taking into account two key factors: the need to maintain the existing plant in operation, and the need to construct the new part of the plant inside the boundary of the site of the existing plant.
The main components of the plant and the works provided are:
- Initial pumping station: demolition of existing station and reconstruction with new geometric dimensions and a new by-pass system with plane gate and ultrasonic system of hydraulic measure
- Nitrification: this aerobic stage provides the biological oxidation of nitrogen, from ammonia (NH3) to nitrite compounds (NO2). The transformation process is due to the activity of Nitrosomonas bacteria colonies. To complete the biological treatments, Nitrospira bacteria colonies convert the nitrite (NO2) to nitrate compounds (NO3)
- Denitrification: in this stage, anoxic conditions are provided, so that heterotrophic bacteria can convert nitrates to nitrogen gas N2
- Secondary sedimentation: a new final clarifier has to be built of equivalent surface area of the existing sedimentation, but with a higher hydraulic head
- Disinfection: in order to discharge back to the environment the treated water, the removal of micro-organism is provided by disinfection. The effectiveness of disinfection depends on the quality of the water being treated (e.g., cloudiness, pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods
The project also envisages building a new sewage interception manhole, consisting of a concrete manhole with internal dimensions of 2.60 x 5.80 m, 4.70 m deep. In this manhole a coarse grid will be installed, consisting of a series of static bars placed between two lateral support structures, placed at an angle of 75 degrees. The vertical bars are 8 mm thick, with a clearance of 20 mm.
The existing pumping station will be completely demolished and the existing pump of 500 m³/h retrieved for temporary phases of work. Four new pumps with a capacity of 150 l/s will be installed in the new pumping station. The pump chamber has the following dimensions: 4.20 x 3.45 m depth 5.70 m.
Denitrification is accomplished by two longitudinal basins with internal dimensions of 45 m x 8,8 m and 4,50m deep, for a net volume of 3564 cubic meters.
The denitrification tanks are equipped with submersible mixers that keep the sludge moving slightly to prevent the deposit of sludge without causing a significant transfer of oxygen. In order to maintain the anoxic conditions, it is important that the mixing speed is kept as low as possible. Three mixers are installed for each tank, with a propeller diameter of 93cm and with a velocity of 157 rpm/min.
Oxidation is carried out in 4 tanks with internal dimensions of 25.40 m x 12.70 m and 4.10 m deep, for a net volume of 5290 cubic meters.
The current aeration system will be replace by installing, in each tank, about 48 panels with long, narrow strips and a large surface area.