What Factors Impact the Purchase Price of a Wastewater Treatment System?

What Factors Influence the Cost of a Wastewater Treatment System?

Volumetric Flow

A common question we ask when evaluating a new wastewater treatment system is, “How much water are we talking about here?”

The flow rate for a wastewater treatment system drives the cost in a number of ways. If the solution involves holding or reaction tanks, those tanks need to be larger, and more expensive, for high flow rates. Pipes and fittings generally get more expensive with size. A one-to-four-inch PVC pipe is inexpensive and almost a non-factor in system cost. When piping gets to six inches and above, the prices increase dramatically, making it an important concern. Valving and the sensor elements for many instruments increase in cost with size as well. As the pipes get larger, the types of valves and actuators may be different from what works with smaller sizes.

The flow of the water also influences the need for redundancy. If a plant is producing only 500 gallons of water per day, it is a smaller problem when the water treatment system fails. Reasonable sized tanks can be brought in to hold water while the problem is troubleshooting, and water might economically be shipped offsite for treatment for a modest period of time. Alternatively, if the flow rate of wastewater is 500 gallons per minute, any failure of the wastewater treatment system will certainly cause an immediate need to shut down production in the plant. In this case more redundancy through multiple treatment “trains” is advisable to ensure continuous plant operation.

Redundancy

Redundancy for wastewater treatment can be considered in three ways:

Redundancy in capacity of a single wastewater treatment train.
Redundancy in multiple treatment trains.
Redundancy in components within a single treatment train.

When planning for redundancy, engineers consider the safety, environmental, and financial consequences of unexpected increases in flow or contamination, failure of a treatment train, and failure of system components.

Water treatment methodologies differ in their ability to adjust to variations in flow and contaminant concentrations. Higher flows and higher concentrations of contaminants often require larger systems. Designers may opt to design a wastewater treatment system that can handle either more water or higher concentrations of contaminants than expected in order to provide some redundancy to a single treatment train.

In the case of an entire treatment system failing, it may be desirable to have one or more additional independent treatment trains available to treat wastewater. If a 100% redundant treatment train is required this is likely to be double the cost of a single treatment train. One way to protect against the failure of an entire treatment train at a lower cost is to have multiple treatment trains at lower than 100% capacity. For example two trains at 50% capacity, or three trains at 33% capacity. These arrangements may save money and space and be enough to keep the plant running in the event of a system failure of one of the trains.

Redundancy can also be thought of in terms of individual components of a single treatment system. In some critical contexts it may be desirable to have multiple instruments taking the same reading at some point if the failure of one of those instruments could cause a significant problem. It may also be desirable to have redundant valving to allow more than one way to restrict or divert flow in the event of a valve failure. Pairing manual shut off valves with critical automated valves is common. Large wastewater treatment systems are typically controlled and monitored through a programmable logic controller (PLC). It is common for systems to have redundant PLC systems to ensure continuous operation in the event of a PLC failure.

Adding redundancy increases system cost and should be considered in the context of the probability and consequences of wastewater production exceeding capacity, or the failure of a treatment system.

Contaminants of Concern

A wide variety of contaminants are found in wastewater. Some contaminants are relatively easy to remove with basic techniques that have existed for thousands of years. Some contaminants are so difficult and expensive to remove that the cost of wastewater treatment endangers the viability of a plant.

A very basic contaminant is suspended solids. Depending on flow and concentration, these can be removed with technologies ranging from a cartridge filter, on the simple end, to a sand filter, or clarifier, at the more expensive range of treatment. In terms of purchase cost per unit flow these technologies are relatively inexpensive.

On the more expensive end of treatment are organic carbon and dissolved metals. Wastewater with high levels of organic carbon contributing to the biological oxygen demand (BOD) wastewater parameter typically require biological wastewater treatment. Biological wastewater treatment will require ponds, or tanks, constructed with aeration distribution pipes and blowers, clarifiers to collect settled sludge, and a filter press to dewater the sludge making it suitable for landfill.

Dissolved metals similarly required multiple pieces of equipment in a process train with a reaction tank to coagulate dissolved metals into solid precipitates, a clarifier to settle those solids, and a filter press to dewater the settled sludge.

Concentration of Contaminants

Limitations on discharging contaminants to sewers and the environment are generally expressed in concentration units like milligrams per liter (mg/L), parts per million (ppm), micrograms per liter (µg/L), and parts per billion (ppb). Most discharge permits allow some concentration of each contaminant.

Higher concentrations of contaminants generally mean more expensive wastewater treatment systems. Removing 100 mg/L of suspended solids (TSS) from a 50 GPM stream is accomplished with a cartridge or bag filter for $7,000. Removing 20,000 mg/L of suspended solids could require a clarifier at $50,000.

In most cases higher concentrations of a contaminant will require a higher priced system.

Stringent Discharge Limitations

Discharge limitations given to regulating agencies are becoming more stringent with time. This is attributed to the greater demand put on sewers and natural waterways by increasing population and industrial activity.

Using the example of dissolved copper, in the past it was fairly typical to see discharge limitations of 1 – 3 mg/L for discharge to a public sewer. More recently, it has been common to see lower discharge limitations of < 1mg/L or even <0.1 mg/L in sewer districts with copper discharge issues.

The challenge this creates is that not all treatment technologies can achieve these low levels of contamination. This may mean an additional polishing process may need to be added to the existing treatment system to remove the remainder of the copper.

For ElectraMet’s fine removal copper cartridges, this may mean running them at a lower flow rate to ensure discharge compliance. This increases the overall number of cartridges and system size. Stringent discharge limitations increase the cost of wastewater treatment systems regardless of the technology used.

Complexity of Contaminants

The term complexity in wastewater generally refers to the number of different contaminants present in the wastewater. Cost for wastewater treatment systems increases as the number of individual types of contaminants increases. This happens because some contaminants must be removed by methods which differ from other contaminants. For example, fat, oil, and grease can be removed by an oil water separator which floats the contaminants over a weir to a collection bin. If this stream also has dissolved metals, they may need to be removed by precipitation and clarification. In this example at least two treatment processes are needed, increasing cost.

In other cases the presence of one contaminant may interfere with the treatment process for another. For example, ElectraMet’s technology electrochemically converts dissolved copper to solid copper by introducing electric current at a specific voltage. If hydrogen peroxide is present in the stream, the electric current introduced will first act on the hydrogen peroxide breaking it into oxygen and water. With high concentrations of hydrogen peroxide a much larger system would be required to both convert all the hydrogen peroxide then capture the copper. For this reason ElectraMet uses Gamma series media technology to pre-treat the stream and decompose the hydrogen peroxide.

In general, the greater the number of contaminants that require treatment, the higher the cost of the wastewater treatment system.

System Location

The location of a wastewater treatment system within a plant, or perhaps outside of it, contributes to the cost of the system. The system being indoors or outdoors is the first important distinction. An outdoor system will generally increase cost by requiring the electrical equipment to be rated for outdoor installation. If operating in a cold climate, heat tracing and insulation may be required for system componentry. In a tropical climate sun shades may be required to preserve PVC piping from sun damage. To achieve an indoor environment outside the plant some systems may be containerized in CONEX boxes. While the containers themselves are relatively inexpensive, this approach has its own expenses in modifying the steel containers for climate control, and providing suitable egress doors and other features to make them habitable according to local building codes.

Indoor installation may also have unique characteristics. Dusty environments may call for special electrical enclosures or protective screens for equipment. Certain hazardous area classifications may call for special ratings in all system componentry. In North America, a class and zone system is used to identify areas where explosions may occur due to the presence of flammable gasses, flammable dust, or flammable fibers. System components rated for these zones must demonstrate that they will not initiate or contribute to an explosion. The high cost of these components generally dictates that every attempt should be made to not locate a wastewater treatment system in one of these areas if at all possible.

Extreme Stream Characteristics

Some wastewater streams are particularly destructive to any equipment attempting to treat it. Extreme stream characteristics include highly acidic, highly caustic, high temperature, and scaling propensities.

Dealing with highly acidic/caustic and high temperature streams adds cost by requiring more durable materials of construction. This might mean piping that is plastic, PFA, or PTFE lined as opposed to basic iron or PVC pipe. This applies to instrumentation, valves, and sensors as well. The pieces of these components that make contact with the liquid are called wetted components. In the case of hot or acidic/caustic streams, these wetted components will need to be of materials suitable for the pH or temperature.

Scaling occurs in piping and equipment where formerly dissolved minerals deposit themselves as solids on surfaces. Dissolved minerals that cause scaling include calcium, magnesium, boron, iron, silicon, manganese, aluminum and others. Keeping scaling to a minimum may require a system to manage pH at a level where minerals stay dissolved. In some cases, maintaining an extremely hot temperature may be required throughout the treatment process to keep minerals in solution. This may require extra heating, heat tracing and insulation for the system, adding to the cost.

Level of Instrumentation and Automation

The price and count of instruments, and actuated components like valves, represent a significant percentage of the cost of a wastewater treatment system. Manually actuated valves are typically a fraction of the cost of actuated valves which incorporate a pneumatic or electrical actuator to automatically turn the valve based on a signal from the PLC. In addition to actuators, a variety of position indicators and sensors are available to monitor the valves position or control their position with varying degrees of accuracy.

Engineers will consider what measurements are required to monitor and control system operation. In wastewater treatment we typically see instrumentation for flow, pressure, oxidation reduction potential (ORP), conductivity, pH, and temperature.

Some instruments can be analog as opposed to digital. For example, we can get a pressure reading with a pressure gauge mounted to the pipe. A great quality pressure gauge may cost $85. If we want to transmit the reading back to the PLC in order to say, move a valve based on the indicated pressure, we would need to use a significantly more expensive digital pressure sensor and transmitter to convert the pressure reading to a 4-20 volt signal and transmit that reading back to the PLC. A digital pressure sensor with transmitter will cost between $800 and $1400 depending on the features and brand.

Instruments that measure the same thing come in different types, and materials of construction. Flow readings alone can be measured by paddlewheel sensors, magnetic flow meters, vortex flow meters, differential pressure flow meters, and visual rotameters. These instruments range in price from several hundred dollars to several thousand dollars.

For every actuated valve, position indicator, and instrument there will be associated costs for installation labor, instrument wiring, pneumatic lines, pneumatic solenoid valves, PLC I/O components, and calibration.

Because actuated components and instrumentation range so dramatically in price, the level of instrumentation and automation is a major factor in wastewater treatment system price. High levels of instrumentation and automation may mean a system that is quadruple the price of a system with limited instrumentation and automation. In rare cases a highly accurate, high quality instrument may itself cost more than the remainder of the equipment.

Pre-Engineered vs. Engineered Solution

A pre-engineered system is a piece of equipment which has already been designed and manufactured in the past. These are “off the shelf models” and they come with existing drawings, parts lists, specifications, and performance characteristics. The design of the system has likely been extensively evaluated and improved for both performance and price. The manufacturer may also have standardized fabrication infrastructure that allows for cost effective production of the unit. If there is pre-engineered equipment which is suitable for your wastewater treatment system this will typically be a lower cost option.

An engineered solution in wastewater treatment means that the system was designed based on specific wastewater stream characteristics and treatment objectives. This process will begin with a design process that creates the system drawings and specifications from scratch. When the system is manufactured it may be the first and only system of this design ever manufactured. With an engineered solution the manufacturer does not have the opportunity to improve design and cost over multiple iterations, though their experience in designing similar systems may mitigate these limitations.

Engineered solutions are generally more expensive, though they may be cost competitive on equipment that is overpriced from off the shelf suppliers. The motivation to purchase an engineered solution is generally to deliver a superior solution in terms of performance in your specific facility. This may mean a system that has a lower operational cost, one which fits in your footprint, or one that meets your requirements for materials of construction.

Budgeting Your Wastewater Treatment Project

As we have seen, a number of factors contribute to the cost of a wastewater treatment system. Trying to understand or budget for a wastewater treatment project can be a daunting task. The worst mistake is to make a guess. A better approach would be to read our two articles on planning a wastewater treatment system (link to part 2 here). FIll out the form below in the footer to get in contact with our team.