WET News

NOVEMBER 2016 WET NEWS 11 TECHKNOW • Five identical 25Ml/d UV reactors installed are low pressure units • Each UV unit has a 316 stainless steel reactor chamber housing 16 800W Amalgam UV lamps • Sludge will be removed by the two lamella sludge transfer pumps • Each wash water holding tank will feature a VSD submersible pump NEED TO KNOW 1 94% of the wastewater discharge from site is generated from backwashing of the existing membrane filters and rapid gravity filters 2 Trant Engineering wants to minimise interference with the operation of the existing membrane filter plant 3 The wash water holding tanks have not been used for 20-plus years 4 The revised design drastically reduced both the construction and operational risks THE VERDICT "The revised design provided greater operational flexibility and security, and enabled the phased migration from the current membrane treatment process to the new UV treatment process whilst delivering considerable totex savings" David Martin, Trant Engineering booster pump, manual and actuated valves together with the associated 316 stainless steel pipework. Each stream also has a dedicated UV local control panel and UPS. Decommissioned Currently, about 94% of the wastewater discharge from site is generated from backwashing of the existing membrane filters (MFs) and rapid gravity filters (RGFs). As the membrane filters are to be decommissioned, recir- culating the RGF wash water flows and would remove the vast majority of wastewater dis- charges off-site. There are 13 RGFs, which periodically require backwash- ing to maintain water quality. The backwash water drains through channels from the filters, through existing cham- bers and currently bypasses two wash water holding tanks before exiting the site. These wash water holding tanks have not been used for 20-plus years, with the manual inlet penstocks to each tank closed, and the manual bypass penstock valve open. These will be refurbished to allow flow to enter the tanks, and an overflow weir will be installed in the reception chamber and the bypass penstock le" open. In each tank there will be a variable speed drive (VSD) submersible pump installed, with a common discharge that will sequentially pump the contents of the tanks to two new lamella thickeners, whereby solids will gravitate into each integral thickener, and supernatant (clarified water) weirs then gravitate to the existing inlet chamber at the head of the works if <10NTU. If supernatant is >10NTU then flow will be directed back to the wash water tanks. Polymer is dosed into the feed line to the lamellas, from dosing plant (D/S Pumps) located within the centrifuge building. Sludge will be removed by the two lamella sludge transfer pumps (D/S) via actuated valves and pumped into the new sludge balancing tank. This tank's contents will be mixed by the new external mixing pump. Two centrifuge feed pumps (D/S) will be installed to feed the two new centrifuges (D/S) located within the new centrifuge building. The sludge will be dewatered to a minimum of 15% dry solids, where the cake drops into a skip beneath the centrifuges. The centrate (liquid waste) is either recycled to the wash water tanks or discharged to the sewer pipeline. Polymer is dosed into the feed line to each centrifuge, from dosing plant (D/S Pumps) located within the centrifuge building. The polymer is made up using makeup units from which the lamella and centrifuge dosing pumps draw from to their respective systems, with the additional facility of being a D/S system. Water supplying the polymer makeup units, polymer dilution (dosing pumps), hose points and centrifuge wash- down is boosted by a new service water booster set located within the UV building. Trant redesigned the original outline design to reduce the need for a second cake reception building, and lessen the aesthetic impact onsite, with a greatly reduced footprint yet still allowing for access to existing water mains and sufficient maintenance access to the new equipment. Site set-up and initial ground investigations have commenced and the works are due to be completed by November 2017. Collaborative working and good communication between Trant and Portsmouth Water is ensuring that Portsmouth Water get the high quality project it demands whilst introducing cost savings and meeting the undertaking date. n David Martin is senior mechanical design engineer at Trant Engineering. NOVEMBER 2016 WET NEWS 11 Concrete's performance is a matter of record. Concrete pipelines are at the heart of drainage infrastructure in many of the UK's biggest cities. They are tough enough to cope with construction traffic and deeper cover depths. They don't lose shape or strength over their service life. They are the strong, stable and sustainable choice. Why pick a lightweight? Precast concrete pipeline Deformed lightweight pipeline 01530 240000 | 028 7964 2558 sales@fpmcann.co.uk fpmcann.co.uk/drainage For details visit: concretepipes.co.uk/heavyweight Modular, multi- parameter water quality monitors for networks t. 0800 8046 062 www.atiuk.com

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