Conference Papers | 2007 NSW Conference Papers

TEMORA SEWERAGE TREATMENT PLANT UPGRADE
Paul Gilchrist, Engineering Works Manager, Temora Shire Council

ABSTRACT

Temora’s Sewerage Treatment Plant was constructed and commissioned around 1930. The plant has given good reliable service over the last 70 years with only minor improvements to the works being implemented over these years. Over recent years however there has been a marked deterioration in the condition of the works and in conjunction with increasing requirement to comply with OH & S & Workcover regulations, and with further reporting required from EPA for licensing, it became imperative that Council address the situation.

1.0       INTRODUCTION

Temora is located in the SouthWest Slopes – Riverina area of New South Wales, 80Km North of Wagga Wagga.

Temora township with a population of 4,600 is a typical rural service centre with major employers being strongly linked to agricultural industries of cereal and oilseed production together with beef, fat lamb, wool production and intensive piggeries. Temora has no significant food processing or other processing type industries.

1.1       Overview of Wastewater Receival and Treatment

The Temora Sewerage Treatment Plant was a Trickling Filter plant constructed and commissioned in 1930 – 31. It was designed with a capacity of 5,200 EP. The works services an area of 400 hectares with a population of 4,600 persons in 1,600 dwellings and businesses.

The reticulation system within Temora is almost entirely gravitation with only three (3) small packaged type pump stations. The Sewerage Treatment Plant is located two (2) kilometres from the town centre.

Treated effluent was, prior to 1970, discharged onto Council owned land (leased for grazing purposes) with excess discharged off site to a watercourse a further 4 kilometres North of the Sewerage Treatment Plant. During the 1970’s a series of ponds were constructed to further process the effluent before discharge off site (see Figure1).

Around 1977 – 78 plans were drawn up and estimates prepared to construct an effluent recycling scheme. This system was commissioned in 1979 with effluent being recycled to the majority of Councils parks and playing fields, together with several third party users. Temora, it is understood, was the second Council in NSW to implement full effluent reuse. Temora’s green playing fields and parks being the envy of many, particularly considering the dry conditions experienced over the last seven (7) years.

1.2       Existing Sewerage Treatment Plant Issues

The existing Sewerage Treatment Plant had performed with minimal problems over the last 70 – 80 years, with generally only routine maintenance and repairs. Upgrading of pumps and installation of a muffin muncher (to reduce pump blockages and maintenance) around 25 years ago, together with upgrade of power supply being major expenditure items. Installation of hand railing, grating, refurbishment of amenities for the operator has also taken place over this period. A back up generator for power supply was also installed in 1999 in response to concerns with “Y2K Bug”.

Over the last 15 years deterioration of pipe work and valves has accelerated, particularly at the digester tanks and the dry well areas. Deterioration and corrosion of walkways, hand railing, grating and access ladders has also occurred with evidence of some “concrete cancer” also appearing. The difficulty of replacing old pipe work and valves and the extent of work required on access and safety items (to comply with OH & S & WorkCover requirements) left Council with a decision – either refurbish the existing works, replace the existing works entirely or upgrade the existing facility. Estimate of cost to repair pipe work, valves and access and safety issues indicated expenditure of around $200K, at least, would be required.

Other issues at the existing works included lack of ventilation, requirement of operator(s) to enter confined spaces on regular basis, continual use of ladders, clearing of sludge drying beds by manual means, lack of automation of processes – leading to requirement for operator to be on site everyday, lack of monitoring of volumes of inflow, wet weather flows and effluent discharged off site (for EPA Licensing). Overall the existing works was an OH & S, WorkCover and administrative nightmare.

2.0       DISCUSSION

2.1       Design and Tender Documentation

Armed with the above information Council engaged Earth Tech to carry out a full investigation and prepare an appropriate design to suit the brief provided by Council.

The design was to include details of geotechnical investigations, full specifications and drawings together with tender documents. These documents would be then ready to distributed to prospective contractors. The plans were assessed by a DEUS (Dept of Energy, Utilities & Sustainability) representative and approval for construction granted. It should be noted here that the project was entirely funded by Council from reserves accumulated in its Sewer Fund – no funding whatsoever was received from DEUS.

Tender documents and specifications were prepared covering:
(i)    Civil Works (including pipe laying)
(ii)   Pumps, Aerators and Inlet Screening including control and monitoring
(iii)  Mechanical Work and Installation
(iv)  Electrical Works

Council indicated that consideration would be given to a contractor that could supply an integrated works together with monitoring and controls to allow the upgraded STP to function without on-site supervision.

Advantages were also seen in having a principle or single contractor to manage the entire project.

2.2       Civil Works

Existing Ponds 1 & 2 (See Figure 1) were put “off line” by diverting effluent flow to pond 4 via a temporary pipeline. This allowed construction of Aerated lagoons 1 & 2 to proceed with additional area adjacent being incorporated into the larger lagoons.

The lagoons were constructed by local earthmoving contractors with Council staff carrying out supervision and quality control. These ponds measure 120m by 80m and are 2.5m in depth. These ponds hold 24ML (see Figure 2). Embankments were lined with geofabric (bidim) and beached with rock to protect the dispersable clay type soil from erosion.

2.3       Inlet Works

The previous inlet works consisted of a manually raked bar screen at inlet side of the Imhoff tanks. This area was accessed by a ladder with raked material transferred to ground level 2.5m above, by bucket.

The design provided by Earth Tech proposed a new inlet channel with mechanical step type screen with a hand raked bar screen provided in overflow or bypass channel. This by pass channel can be isolated and is used during maintenance of the mechanical screen and to accept flood flows and other high flow situations.

After visiting several other recently upgraded STP’s at Cootamundra, Mt Beauty, Bright and Mytrleford and assessing the performance, maintenance requirements and ease of cleaning of various inlets screens, including step screens and spiral or auger type screens, it was decided to utilise a spiral type screen for the Temora plant.

Advantages were seen as:
(i)   ease of installation and commissioning
(ii)  ease of maintenance
(iii) ability to handle flows up to 130L/s
(iv) suitability for smaller type plants

To date after 27 months operation, the only maintenance has been the replacement of the nylon brush on periphery of the spiral (cost $1,800) together with fortnightly pressure cleaning of channel walls to remove grease and grit buildup.

The screened waste material is deposited in a sulo bin (see Figure 3) for pick up by Councils Waste Management Staff and transfer to landfill. The volume of waste material being around 60 litres/week.

2.4       Relift Pump Station

The existing pump station comprised two wet wells with outlets to a dry well which housed pumps to deliver effluent to the pond system.

The dry well housing the pumps had a depth of 4.5m and any valve or pump maintenance required confined space entry. This maintenance had recently become a regular event especially with the deterioration of valves meaning that flow could not be stopped to isolate the pumps. Dry well flooding had occurred on several occasions in the last few years due to blackouts or failure of float switches, resulting in burnt out electric motors.

The new pump station arrangement utilises the existing two wet wells with a splitter manifold. The splitter has been with valves to enable isolation of each well (see Figure 4). Each side of fitted wet well has been equipped with two (2), 8kw Submersible pumps. These pumps are mounted on rails and can be removed for servicing and maintenance without entering the wells.

Discharge pipe work from the new pumps was installed and penetrates the floor of the existing pump house structure to enter a manifold for discharge to Aeration Lagoon 1 or Lagoon 2.

The pumps are controlled for alternate running and designed for redundancy should a failure occur outside of normal or routine maintenance. The average dry weather flow is 12L/sec with peak wet weather flow nominated as 30L/sec.

The old dry well pumps were removed, with old valves sealed off by the pouring of a new concrete base in the wet well. The dry well was then sealed off and plays no part in the upgraded Sewerage Treatment Plan.

The existing Sewerage Treatment Plant had no monitoring or automated controls (apart from float switches). All operational functions of the old Sewerage Treatment Plant were carried out by hand and required an employee to be on site seven (7) days per week.

The monitoring and controls included in the upgrade are considered the most important aspect of the project. The monitoring and control system is based around ITT Flygts FMC-639 remote terminal unit for the control and supervision of wastewater pump station equipped with one or more pumps (see Figure 5). The remote terminal unit incorporates a processor, data memory, program memory, alarm panel, display and level transmitter. The remote terminal unit is equipped with a modem and back up power supply. The unit is also equipped with parameter-controlled functions for pump control, alarms, operating statistics and performance monitoring as well as communication with a central system and/or paging system. This system can be then monitored at a desktop utilising the ITT Flygts Aqua View program.          

Recently the system has been improved to allow monitoring via the internet. The Aqua View program enables set points for all functions to be monitored and changed if required, from any computer, with Aqua View installed, and with internet access. All data including pump starts, pump run time, sump levels, inlet chase level, inlet screen run times can be changed remotely and data stored. Reports and graphs can also be generated for the above functions as well as effluent volumes received and effluent volumes pumped for reuse.

3.0       CONCLUSION

3.1       Positive Aspects of Upgrade

• Control and monitoring carried out remotely
• Simplicity of operation and function of upgraded works
• Saving in labour costs ($75K/year) – lower operating costs
• Saving in energy costs (10%/year) – lower operating costs
• EPA monitoring requirements met or exceeded
• Fault communication system allows maintenance to be planned
• Fault communication system allows only critical failures to be attended to after hours
• No requirement by maintenance personnel to enter confined space
• Expandable System to allow additional pumps or equipment to be added and monitored in future
• System has spare capacity for town growth
• No requirement for OH & S upgrades
• Reports can highlight system problems e.g. filtration after rainfall events

3.2       Future Directions

These upgrading works carried out at total cost of $780K allows Council time to analyse and assess future requirements that various regulatory authorities may place on Council in the medium term. It also permanently alleviated OH & S and WorkCover concerns. It will also allow Council’s new pricing structure to build reserves for the next phase of Sewerage Treatment Plant upgrades that will take into account more stringent environmental requirements.

4.0       ACKNOWLEDGEMENTS

ITT Flygt with special thanks to Rob Carney for this assistance throughout this project.

Temora Shire Council staff in Plant Management and Parks Management whose assistance and patience helped throughout this project.