Meeting the DBO challenge

Public-Private Partnerships has created a trend towards inclusive contract arrangements that reflect the complexity of modern project management. Many contracts now involve the integration of design, build and operation, says David Parsons.

A wastewater treatment works (WwTW) can be viewed in several ways, such as a high-tech processing plant using the latest SCADA systems and wireless links to remote engineers to minimise on-site manpower. In this technological view it is usual to concentrate on the plant’s efficiency in terms of its ability to remove the waste products and return a compliant water stream back into the ecosystem.

Other IT considerations will include energy conservation, minimisation of water leakage, and good neighbour activities such as odour control.

The WwTW is a hub. Its purpose is to act as the filtration system and further treatment facility for wastewater piped into it, or delivered to it by road tankers. After processing, the WwTW also serves as the depot from which treated biosolids are taken for recycling to land, incineration or landfill.

You might see the business as being a logistics exercise to maintain a mass balance across the works. An Information & Communication Technology (ICT) view might be that the data available there could be considered as a Management Information System (MIS) that is necessary for local process optimisation. But, data needs to be pushed up through vertical integration to become part of the corporate ERP system.

This means that data should be directly relevant to the ERP function, reflecting the business KPIs and legislative needs but resisting the temptation to dump plant SCADA data onto the corporate LAN just because its readily available.

Although some have argued for an integrated approach, the complex and segmented nature of the wastewater treatment business has led to the adoption of these and other views and there has been no particular driver to bring about convergence – until now. So who needs to take a fully integrated approach to sludge treatment and biosolid recycling? The answer is the DBO contractor.

The key issues can be expected to remain within three areas – collection, treatment and

disposal. Sewerage networks, initially appropriate to the local population, will serve most recycling plants and require expansion to accommodate increases in population equivalent (PE). Most of the bigger recycling centres will act as designated reception points for tankered domestic waste (TDW), trade waste and inter-site transfers from smaller works where upgrades are still uneconomic. This diverse and often highly variable input into the process raises a number of questions about the product including:

  • What is it?
  • How much of it is there?
  • Where did it come from?
  • When was it collected?
  • How did it get here?
  • Can we handle it in this quantity and composition?

Despite its high design and build cost, the traditional treatment works is relatively simple. Initially the inlet section of the works screens off the “litter” and removes grit before the wastewater flows into the primary treatment area, which is usually a settlement tank.

A secondary stage uses micro-organisms that obtain their nutrient from the wastewater to further decrease the BOD and produce secondary sludge. In high performance processes this is subjected to further treatment, maybe using chemicals, to precipitate a tertiary sludge and leave cleaner effluent water.

Sludge is drawn off and allowed to thicken in settling tanks. The rest of the processing depends on the destination of the excess treated sludge.

The steady state conditions can be disturbed by a rain storm, causing a rapid increase in the inlet volume, or an unexpected number of road tankers arriving at the same time or worse of all a batch of polluting material getting added to the process.

This might be actually toxic to the micro-organisms, which could be disastrous, or even if it is harmless, but very dilute, it could imbalance the process yielding liquid sludge when cake was intended. The Urban Waste Water Treatment Directive ended the practice of using the sea as a disposal route for sludge. At the time – December 1998 – this was how 17% of UK sewage sludge was disposed of. UK figures for 2004 suggest 66% of biosolids were recycled to land for agricultural use, of which 4% of crops were classed as industrial.

Some 19% were incinerated and 11% used for land reclamation, forestry and compost. Only 1% went to landfill, down from 15% in 1998. No disposal route is without its critics but the controlled recycling of treated biosolids to land is seen by many to be the most environmentally-friendly option, providing that food safety issues are addressed.

European directives have been voluntarily surpassed in the UK by the introduction of the Safe Sludge Matrix and Code of Practice for Agricultural Use of Sewage Sludge. Since 2003, this has included the application of hazard analysis critical control point (HACCP) procedures to the guide for good recycling practice so that the Food Industry would feel more at home with the controls.

Audit trail

This approach is the underpinning concept of Bio-Trak, an integrated management system that lends itself to the DBO project philosophy. Bio-Trak started life as an automatic audit trail system to comply with the EU directive designed to control the application of sewage sludge to agricultural land.

The extension of the audit trail to include the collection of sludge for processing and then plotting its progress through the treatment plant was proposed later. For a typical UK water company this presents a challenge due to legacy plant and systems. Sludge might have to be removed from a 1,000 small sewage works where nature cannot do its work fast enough.

This might be collected by the water company’s own transport, under framework agreement and/or ad-hoc third-party contracts. Also, there is likely to be domestic waste collected from septic tanks, cesspools and chemical toilets and delivered by a wide range of vehicles.

It looks impossible to automate the collection and integration of the various sets of control data. This is why Bio-Trak takes a modular approach and offers choices to cater for the individual requirements of legacy operations that cannot be cost-effectively changed.

Other underpinning objectives of Bio-Trak were to make data collection easy and not to expect too much from operators of the system. It has, for instance, proved to be far more convenient to have the collection point information confirmed by automatic GPS than to require a tanker driver to select from a drop-down menu,or manually input the details.

Cost is always an issue. If the need is to design hardware for sludge collection data from 1,000 outlining sites, for delivery to 40 major recycling plants, using 50 road tankers, then the most efficient solution is to put the significant hardware on the tankers and in the key processing hubs. Each of the main works is already likely to be a node on the corporate IT network, therefore offering an existing route to the MIS.

Installation costs are likely to be very significant so a battery-operated wireless device that avoids higher civil engineering costs and minimises health and safety considerations often proves the best overall solution.

A telematics system is fitted to all of the vehicles, both in-house and contractors involved in the operation of the wastewater recycling business. Functionality would include getting answers to the questions raised, providing an audit trail with little or no driver intervention.

Now consider what would happen if the “mobile” data is made available automatically, by real-time wireless transfers, to be combined with other input data, from flowmeters set in pipes, open-channels and fed into to the SCADA system. This means that extra controls can be added, and algorithms can be fine-tuned, to maintain an efficient flow through process. Such automation requires high security and, even at sparsely populated plants, only authorised users should be able to enter the works and take a particular type of load to a designated entry point into the process. The load can be measured and monitored on a flow through basis so that online alarms can be raised and problem loads attributed to the correct source. Now assume that the overlapping telematics and SCADA platforms also operate for loads leaving the plant with treated biosolids. This allows the Bio-Trak system to provide the audit trail for the disposal routes as well.

Improved efficiencies

It is much easier to extract useful business information, to improve efficiencies on the logistics side, help to make decisions on future works upgrades and give the clearest picture yet on the environmental implications of the operation. Using the Bio-Trak approach it has been possible to ensure that relevant data flow is automatic, secure and directed to the MIS where it is needed. Ongoing operational improvements, in such key high profile areas as logistics, energy usage, water minimisation and environmental safety, can be accommodated. Such an integrated package represents a significant reduction in business risk to both the client and the DBO contractor.

David Parsons is customer support & business development manager at Meteor Communications (Europe).

T: 01727 828200.

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