Wastewater Designers & Installers > Large Scale Projects
Large Scale Projects
AES systems are well suited to large scale projects with their OSET-NTP tested high levels of treatment, flexibility of design to meet specific conditions and Council Compliance. AES has been used on some very large projects overseas including a town of 200 homes in the USA. It is increasingly being used on large projects in New Zealand. Please contact us to discuss your project.
Lake Mahinapua DOC camping ground
Lake Mahinapua DOC camping ground, south of Hokitika, required an upgrade of its existing wastewater system servicing a toilet block via septic tank primary treatment to low-pressure effluent dosing into a gravel filter, to cater for the addition of a new shower block.
The original system was designed 17 years ago in accordance with Auckland Council’s ‘Technical Publication #58: 1994 On-site Wastewater Systems: Design and Management Manual’ with the design based on a high infiltration rate of 130mm/day. The current 2004 version of TP58 does not recommend high DLR’s for primary treated effluent. High infiltration rates in TP58 now require effluent to be treated to secondary standard prior to discharge to land.
Stuart Challenger of Eliot Sinclair, as wastewater designer, recommended that the land application bed be upgraded to an AES treatment disposal system with effluent from the existing septic tank pumped to 6000L of additional septic tankage to match the expected additional inflow from the shower block and then be gravity fed to the AES treatment bed via a 4-port distribution box (a 7-hole box was actually installed for future-proofing). Provision is included for buffering the pump derived outflow through the septic tank prior to the distribution box, to be less than 76 litres/minute from each box port.
The new shower block will increase the daily flow from 30 to 50L per person. Peak design inflow for 300 people is 15,000L.
Inclusion of the grey water from the showers helps to dilute the effluent similar to domestic strength than the higher strength primary treated black water previously discharged. As the maximum design flow will be maintained for only a short period over Christmas / New Year, using an AES loading rate of 55L/m for the design of the AES bed was deemed appropriate. This was based on the tested performance of the AES system in Trial 12 at Rotorua’s OSET-NTP facility. During this trial at 200% loading for 5 days or 76L/m of AES pipe, there was no significant impact upon BOD, with TSS still maintaining A+ grading and minimal impact on nitrogen reduction.
At both the 38 and 76L/m loading AES is recorded at OSET performing better than almost all AWTS package treatment plants. Check the recorded performance here.
Click on the image below to enlarge.
The number of AES pipes required was 15,000L/55L per m = 273m divided by 3m (= length of AES pipes) = 91. The current location for the land application bed was about 20m long so with 6 pipes in each row the length of the AES bed would be 18.6m and the number of rows would be: 91/6 = 16 rows (actual rows would be 15.2 but as it is not recommended to have part rows, this was rounded up to 16). So the width of the bed is 16 rows x 0.45m per row + 0.45 for side clearance = 7.65m. The total area of the bed is therefore 18.6 x 7.65 = 142.3m2. This is a loading rate of 15,000L per day/142.3 m2 = 105mm/day.
This is a lower application rate than the previous 130L/day. The AES bed is located so that it can be extended lengthwise or sideways at a later date if required using the unused ports of the installed 7-port distribution box.
The septic tank capacity needed to be increased by a similar amount to the increase in inflow to have capacity for 24 hours storage plus room for build-up of scum and sludge. i.e. 20L/person/day x 300people = 6000L. A 9000L septic tank was installed adjacent to the existing tank and above the beds to allow for future increased use. As the effluent is pumped to the additional septic tank it was recommended that the filter be removed from the existing tank to allow some of the solid matter through. From the new septic tank, the effluent flows by gravity to the AES bed. However, the outflow from this additional septic tank is at the same rate as the inflow so it was necessary to buffer the flow before it enters the AES bed. A 2m section of 200mm dia pipe was installed prior to a 90-degree bend before the distribution box. Installation was managed by Duncan Hamilton of Dwan & Andrews from Hokitika.
Wooden staples securely hold the 4 rows of AES pipe split into 4 sections placed on a base of 300mm system sand ready for the surrounding and covering sand to be added. Access to the bed was only available from the far end. The staples were lifted and re-established as the construction of the bed progressed when the covering sand was flush with the top of the 150mm top boards of the staple. Note the use of 2 position staples in this manner in securing the AES pipes in a wide bed.
The completed AES combined treatment and disposal bed showing the raised connector pipework fitted to the offset adaptors on the ends of the sections of each pipe row. All venting was manifolded at the septic tank end. The work was completed with a 20 ton digger and 4 staff in 6.5 hours. The AES system sand was stockpiled about 20 metres distant from the end of the bed.
Hillsborough Hideaway – a large AES installation featuring distribution to 4 separate pipe beds
Hillsborough Hideaway near New Plymouth is a large rural property with a range of amenities; a house, a luxury 2-bedroom rental apartment, heated pool, tennis courts, and adventure playground. In addition, a museum is being built to showcase a variety of Holden cars and memorabilia, with an adjacent restaurant.
The existing septic tank and field for the house and apartment needed to be upgraded for the accommodation, museum and restaurant. The owner chose AES because it is an environmentally friendly and cost-effective option that could be retro-fitted to the existing system. On a sloping hillside section with a mix of soil types, the obvious site for the new septic tank, pipes and field was on the lower slopes near the road.
The wastewater system needed to be designed for a maximum daily flow of 9195 litres per day; equivalent to a per day maximum of 220 restaurant diners, 100 visitors and 11 people residing in the house & homestay.
To manage this load, the Wastewater system designer Kama Burwell of Greenbridge Design & Implementation, chose to install four separate pipe beds, level and perpendicular to the slope with each bed stepping down the gentle slope. A distribution box on the outflow from the new 25,000L septic tank sends equal amounts of flow to each pipe bed. Each bed consists of two rows of three lengths of pipe with raised connectors between each row, providing 60m of treatment pipe length in each pipe bed.
AES provides distribution boxes for this type of design and can offer technical advice for your situation if you wish to use this feature. It is ideal for wastewater treatment on large scale projects.
A Large scale Town AES installation – 200000L per day in cold temperatures
The Blodgett Landing Treatment Plant is in Newbury in the southwestern part of New Hampshire. In 2001, the town started detecting elevated nitrogen levels within the effluent and ground water. They lined the original sand filters so they could catch the effluent and pump it into a recycling tank. 50% of that effluent was recirculated to an Imhoff tank where organic material aided in reducing the nitrogen and ammonia.
However, they still had issues with attaining treatment in the winter months as well as other long term problems. The town identified the following four major issues:
- winter operation – parts of the system would routinely freeze, hindering its operation
- the cold weather also affected the treatment levels
- increased de-nitrification requirements
- a growing community required a system with increased capacity
After investigating many options, in 2010 the town chose the Advanced Enviro-Septic® Technology for their treatment needs. As a passive wastewater treatment system tested and proven to remove up to 99% of wastewater contaminants such as BOD, TSS, TN, TKN, and Faecal Coliforms it surpassed the standards required. Enviro-Septic® Systems have proven effective in cold weather. The warm effluent combined with the biological process that takes place within the pipe generates enough heat to keep the system from freezing. The Newbury Blodgett Landing treatment plant is designed as a re-circulating system with the patented Multi-Level™ configuration handling flows ranging from 9,464 – 333,115 L/d.
After the wastewater is received, it goes through an initial screening and then proceeds to one of two Imhoff tanks where sedimentation and separation occurs. After the Imhoff tank, the effluent then proceeds to an equalization tank before it is dispersed to one of the four passive Enviro-Septic® treatment beds.
Each treatment bed measures approximately 90 feet long by 50 feet wide. The beds consist of 48 rows of pipe that are each 86 feet long. That means there is approximately 4,100 feet of pipe per bed or roughly 16,400 feet for the entire system. At 50,000 GPD the 16,400 feet of Enviro-Septic® pipe treats roughly 3 gallons per linear foot per day. With an impressive 25 sq ft of surface area per linear foot of EnviroSeptic®, you have over 400,000 ft2 or over 9 acres of bacterial surface area in this system. A large amount of bacterial surface combined with sufficient oxygen and other patented features allows for high levels of treatment. These treatment beds are lined to capture the treated effluent. Once captured, the treated effluent is then pumped into a recycling tank. 75% of the treated effluent is then sent back through the Imhoff tanks via recirculation pumps and the rest is dosed into the dispersal area. As the treated effluent that is sent back to the Imhoff tanks goes anaerobic, the organic material present acts as a carbon donor in the denitrification process. Additional denitrification then takes place in the anoxic zone of the Imhoff tank.
In addition, large flow industry projects are looking for wastewater treatment options that don’t require pumps, chemicals, ongoing maintenance and alarm systems that add to staff requirements.
The following test results are averages of samples taken at the re-circulation chamber.
The town of Newbury has been very pleased with the performance and operation of this system. Plant Manager Tim Mulder said,
“Since it was installed in 2011, the system has consistently exceeded the required effluent treatment levels. The upfront cost saving of this technology along with its ability to perform with minimal ongoing cost and maintenance makes it truly exceptional in the world of large-flow wastewater treatment.”
Plant Manager, Tim Mulder
