First Rainwater Treatment Systems and Tanks

Introduction

Managing first rainfall is one of the main objectives to protect ground water. Specifically, these systems are designed to temporarily store (in precast tanks) first rainwater, with a timer-controlled and delayed delivery (about 48 hours) after rain stop through an electric lifter pump for the following treatment (static oil separator with coalescence filter).
The use of these system aims at reducing surface water pollution and mitigate flood peaks caused by heavy rain (rain bombs).

Features and operating principle

First rainwater coming from the sewage collecting all water from roads, car parks (transit areas), is channeled into storage tanks via a spillway or bypass, and this system separates first rainwater - "potentially polluted waters identified in the first 5 mm" - from second rainfall, supposed to be clean and not contaminated, therefore ready to be channeled into the outlet.
First rainwater is temporarily collected in precast reinforced concrete tanks where sand and sludge sedimentation takes place, first and second rainwater separation is ensured by a stainless steel floater anti-backflow valve mounted on the storage tank inlet and then (usually after 48-72-96 hours) they are sent through to an oil separation treatment for light fluids (discharge table 3) thanks to a submerged electric pump with constant flow rate, or, alternatively, to the final collector.
Sometimes, if the limits required by the operator are particularly strict (discharge table 4), it is necessary to thoroughly treat water, and therefore quartzite and/or activated carbon filters are installed.
After the treatment, it is necessary to always have a sampling pit with suitable dimensions to take samples.
The competent body for final receptor management (public sewers) can require the installation of a flow meter to quantify discharged first rainwater.

Accessories suggested to control pollutants

SET\DM3DL Digital Conductivity Probe

The oil interface probe SET\DM3DL is installed in the collection compartment for light slurry at a pre-set height.
The probe triggers the warning system if its upper part section is reached by oil or hydrocarbons. The probe is usually submerged when operating.

SET\S2 Digital Ultrasound Probe

The sludge warning probe SET\S2 is installed in the lower portion of the separator. The probe activates the warning system is the sand or sludge layer reaches it. The probe is usually submerged when operating.

SET1V Digital Vibration Probe

The SET\V limit threshold probe is installed over the highest tank level. The probe triggers the warning system if reached by fluids (water, oil, other). The probe is usually hanging when operating, with no contact with fluids.

Supply Specifications

Delivery and installation of First Rainwater System manufactured in DECLARED SERIES Mod. RAIN____ system with storage of the first 5 mm rain and delivery to the external oil separator, surface _____ sqm, effective volume ____ cubic meters, DN pipe cross-section ______, external oil separator NS flow rate ____ lt/sec suitable for treatment system, composed of underground precast tanks manufactured by EDIL IMPIANTI 2 S.r.l. with UNI EN ISO 9001 and ISO 45001 management system made of monoblock vibrated concrete, reinforced with vertical pillars and stainless steel horizontal beams, with CE-certified materials, concrete in compressive strength class C45/55 (RCK >55 N/mm²), internal improved-adhesion steel reinforcements checked in our plant, GREESMIX5® steel fibers (patent No. 0001421398 issued by the Ministry for Economic Development) and electro-welded square mesh B450C, with certification of CHEMICAL RESISTANCE and REACTION TO FIRE (Class A1) issued by an external body based on UNI EN standards.

The First Rainwater System Mod. RAIN_____ The system with 5mm first rainfall storage and delivery to the external oil separator must include:
- External spillway, dimensions ______ x ____ x ____ cm height, with inlets, bypass, and outlets to First Rainwater Tank;
- Precast First Rainwater Tank/Tanks for sedimentation and storage in monoblock vibrated reinforced concrete. External dimensions _____ x _____ x_____ h cm for an effective total volume of ____ cubic meters, with inlet and inner inlet AISI 304 stainless steel shutter valves, vibrated reinforced concrete partition wall to protect the electric pump/s, outlet for pump/s delivery, First Rainwater package with 1/2 electric pump/s, rain sensor, switchboard and optical-acoustic warning.
- Static oil separator Mod. DISCE _______-FC CE-marked and UNI EN 858-1 compliant, NS flow rate ____ lt/sec, external dimensions _____ x ____ x ____ h cm, with inlets/outlets, inlet coupling connection with elastomeric rubber gasket and calm AISI 304 stainless steel baffle, removable and washable refill coalescence filter with AISI 304 stainless steel frame, automatic floating shutter entirely made of AISI 304 stainless steel.
All tank external walls must be waterproofed with suitable coating materials.