The Church of Jesus Christ of Latter Day Saints runs one of the largest schools in Tonga. The school offers an excellent level of education to the local Tongan community and now teaches more than 1000 students, including at least 200 students that board full time at the school. Built in the 1960’s, the school is located in Liahona which is approximately 30 minutes drive from the capital Nuku’alofa.
The existing wastewater system to treat the effluent from the school was also built in the 1960s and consisted of a gravity sewer pipeline discharging to a pump chamber which transferred the wastewater into two large aeration ponds before discharging into soakage trenches. Located approximately 300 metres from the school grounds, the average daily flow into the ponds is 150,000 litres per day with peak flows of 200,000 litres/day.
After more than 40 years of use, this system was at the end of it’s working life and a substantial refurbishment was required to upgrade the system to provide a suitable level of treatment for the schools wastewater.
In July 2004, Beca International Ltd were appointed by the Church to develop a specification for a new pump station and treatment plant to treat the wastewater from the site.
The first option identified was to pump out and re-line the existing ponds. The cost of this option however, proved to be more expensive than building a new treatment plant. The decision was then made to identify wastewater specialist companies capable of designing and building a suitable plant at the school. The existing ponds would eventually be de-commissioned and filled in so the land could be used for alternative uses.
In August 2007, five wastewater companies from New Zealand and Australia were invited to visit the school to assess the site conditions, meet the client and evaluate the local civil contractors who would be completing the construction of the concrete structures on site. Tenders were then required to submitted to Beca International Ltd by 30 October 2007.
After the submission of the initial tenders, two companies were invited to re-design and re-tender the project to bring it within the Church’s budget.
Hynds Environmental designed a twin stream Submerged Aerated Filtration (SAF) wastewater system utilising a total of nine precast water tanks manufactured in New Zealand from “Hydura” acid resistant concrete. This revised design was the only system to meet the on-site requirements and also meet the budgetary constraints for the project.
Hynds Environmental installed all the internal aeration, filtration and electrical components into the tanks in Auckland before transporting them to the Ports of Auckland. They were then loaded onto three 40 foot flat racks and lifted onto the deck of the Southern Lily which landed in Nuku’alofa on the 2 July 2008.
Once the tanks were off-loaded safely in Tonga, the challenge was then to transport them to site and lift them into position while incurring no damage to the tanks. Hynds Environmental worked closely with Reef Shipping and Fletcher Royco to ensure that this process was achieved successfully and efficiently using a local trucking company and Fletcher Royco’s mobile crane.
Once the tanks were all in place, the Hynds Environmental Operations team then completed the construction and commissioning of the wastewater system on site in just three weeks.
“Hynds Environmental were excellent to work with” said Chris French, Project Engineer for Beca International Ltd who was on site for the final stage of construction and commissioning of the system “they were extremely efficient, professional and the level of workmanship they produced was outstanding”.
Beca International Ltd were also impressed with the design and functionality of the system. “The design for this project was perfectly suited for this application” said Chris French “Hynds Environmental were very innovative and the final design is simple to operate and maintain which is vital for this application”.
The system is now operating perfectly on site, has achieved practical completion and The Church of Jesus Christ of Latter Day Saints are extremely pleased with their new wastewater treatment plant. “This has been an excellent team to work with” said David Amende, Project Manager for the Church “Hynds Environmental, Beca International Ltd and the Church worked really well together to produce a great result for the school”.
For further information on Hynds Commercial wastewater Systems, contact Hynds Environmental on 0800 425 433 or visit www.hynds.co.nz.
Plant Specifications
The specifications for this plant included the following
Ø Average daily flow of 150,000 litres / day
Ø Peak daily flow of 200,000 litres /day
Ø Supply and install of a new pump station
Ø Primary screening of the wastewater
Ø Secondary treatment to 20 mg/l BOD5 and Suspended Solids
Ø Two stage submerged aeration filtration treatment process
Ø Discharge into new soakage beds on-site