In the first part of this series, we reviewed the factors that engineers considered when determining the process by which wastewater will be treated. We limited our discussion to process factors like the volume of water, contaminants that will be removed, and where the water will go after treatment.   

This initial analysis may present us with several types of industrial wastewater treatment which will have differing advantages depending on the context of the plant location, and the associated availability of resources like utilities, services, and space.

In this second part, we will review decision factors that will be specific to each individual facility. We’ll organize our thoughts into the following categories:

• Available utilities
• Discharge options
• Plant location
• Footprint availability

Available Utilities

Fresh Water

It often takes some amount of fresh water to treat wastewater. Sand filters, ultrafiltration systems, and other filtration technologies often require an external source of water to accomplish backwashes. Some chemicals used in precipitation will be supplied as solids and must be dissolved in a make down tank before being introduced to the reactor tank. Regenerating ion exchange systems will require fresh water to mix with concentrated caustic and acid to perform regeneration.

Planning your wastewater treatment system includes determining the quantity and quality of fresh water required for the treatment process, and determining the cost of water whether it comes from public supply, a well, or treated surface water.

Power

Engineers should review the power requirements for the various equipment in their proposed wastewater treatment system.

Typical equipment that uses significant power in wastewater treatment systems are mixers, blowers, pumps, and larger electrochemical systems.

Electrical supply is rated by frequency, phase, and voltage. In North America, power is delivered at 60 Hz, single phase and 3-phase, 120V, 240V, and 480V. Outside North America 50 Hz power is more common and the available voltages may differ. In actuality the voltage in a line may fluctuate depending on the load and quality of the local grid.

When you review the power requirements for equipment the voltages are typically given as the minimum voltage for safe operation. These may be expressed with numbers like 110V, 230V, and 460V. It is critical that you determine the availability of the correct type of power supply. While most large industrial facilities have all types of available power, a smaller facility in a less industrialized neighborhood may not.

Extremely large facilities may need to consult with local power authorities to confirm the availability of large quantities of current, and additional infrastructure like a small substation may be required.

When the type of power available has been determined, it is advisable to estimate the total power usage. Most significant loads of power will be associated with motor driven equipment, mixers, blowers, pumps, etc. An expedient way to estimate power usage is to inventory the HP ratings of these motors multiplied by their relative efficiencies, add them together, and multiply by 0.7457 to calculate kilowatts.

A cost for electrical power should be determined in consultation with the local power providers. This is usually expressed in dollars per kilowatt hour. At the time of this writing, the average price per kilowatt hour in the United States is fluctuating around $0.15 per kilowatt, hour but in some regions the price could be 3 times this amount.

Certain components of water treatment systems, PLCs, instrument electrical signals, and electrically driven valves don’t use a significant quantity of electricity and could be excluded from the analysis.

Natural Gas

Natural gas is a relatively low-cost fuel which can be burned to produce heat. It is used in wastewater treatment processes to either directly heat evaporators and crystallizers, or as a fuel to generate steam to power this equipment.

Engineers should determine the quantity and cost of natural gas required to power their processes and consider this in the operational expense of the system.

The availability of natural gas should be considered as well. If the local infrastructure does not exist for sufficient supply, the construction of purpose built natural gas lines is often prohibitively expensive.

Natural gas is a valuable byproduct of some wastewater treatment plants. Anaerobic digestion plants are biological wastewater treatment systems which use microorganisms to consume and break down organic contaminants. Some species of these microorganisms emit methane, carbon dioxide, and water as the waste products of their metabolism.

In smaller systems this biogas is either vented to the environment or flared. In larger systems it can be possible to capture and purify the methane for reuse in the plant. In this way the natural gas produced becomes a credit against the operational costs of the system.

Steam

Steam is used in various wastewater treatment methodologies like steam stripping of volatile organic compounds, clean in place systems, and in heat exchangers for hot water sanitation processes. 

Steam is typically rated by pressure ranging from 150 psi for small applications to 3,000 psi in some power plant applications.

To include a steam driven treatment process you will need to ensure that there is a boiler onsite that can produce the correct pressure and quantity of steam for the equipment.

Steam quantity is typically measured in pounds or kg per hour. To determine cost inputs, it will be necessary to work with the steam plant operators or equipment suppliers to determine a cost per pound or kg.
If a steam plant does not already exist onsite, this will be a significant addition to the capital expense of the project.

Compressed Air 

Many industrial systems, including wastewater treatment systems, utilize compressed air. In industrial wastewater, compressed air is used to actuate valves, air scour sand filtration beds, generate bubbles in dissolved air flotation systems, and air scour some membrane surfaces.

The compressed air specifications for each piece of equipment should be reviewed to ensure that air can be supplied at the correct pressure and quantity. Some applications like pneumatic valve actuation will require instrument air, compressed air that is free of particulate, moisture, and oil.

For simple actuation of valves, the operating expense for compressed air will be minimal. If compressed air is being utilized for generating bubbles, or frequent air scours, it should be considered in the operating expense of the system.

Discharge Options

Sewer Discharge (Publicly Operated Treatment Works (POTW))

If a sewer discharge is readily available, this is usually an attractive option. Engineers should consider the cost per unit volume of sewer discharge and any discharge limitations on individual contaminants.

Sewer authorities typically have two types of discharge limitations. The first type of limitation is absolute. You cannot discharge more of this substance than allowed or they will fine you and may ultimately shut off your ability to discharge. The second type of limitation are those which you can exceed but will be surcharged for. For example, there may be a concentration limit of 400 mg/L BOD but you can discharge up to 10,000 mg/L BOD if you pay a surcharge on the pounds of BOD generated beyond your 400 mg/L concentration limit.

Absolute limits and surcharge ranges will vary from district to district, usually depending on how much extra capacity the local sewer plant has and their own costs of treatment.

In the example above an engineer should compare the cost of paying a surcharge for BOD exceeding 400 mg/L with the cost of additional treatment to achieve this limit.

Making early contact with the local sewer authority is critical for planning a wastewater treatment system. To provide a real-world example, a manufacturer received a large government grant to build a new plant in a remote and rural area. However, late in the planning process, they discovered that the local sewer facility lacked the capacity to treat their wastewater and could not handle the projected water volume, even after pre-treatment. As a result, the manufacturer was forced to help upgrade the local municipal capacity, incurring significant delays and additional costs.

Discharge to the Environment

Discharge to the environment means piping treated wastewater to a nearby ocean, lake, river, stream, intermittent ditch, or even application over dry land. For any of these options a National Pollutant Discharge Elimination System (NPDES) permit will be required. Depending on the location, there may be an additional state, and even a local permit required.

To obtain a permit, it is important to start the application process early. It is highly recommended to engage an experienced environmental consultant with local experience to guide you through the process.

Plant Location

Plant location, climate, and geography is an important factor in wastewater treatment design.

Plant location

The location of the plant determines the availability of discharge options. In order to discharge to a sewer system or a water way, one must exist in proximity to the plant. Running a pipeline long distances to a sewer or waterway can be extremely expensive and should be considered and evaluated early on.

There are a number of external costs involved with treating wastewater. Some of these are necessary reagents like sulfuric acid, hydrochloric acid, sodium hydroxide, lime, coagulants, and polymers. There are also shipping and disposal services for dewatered sludge and liquid waste. These costs can vary dramatically between regions depending on distance to the manufacturer or service provider, availability, and local production costs. This may affect your decision on how to treat your wastewater. Local costs for these supplies should be obtained during the planning process.

Climate

Local climate is particularly important if an outdoor installation is required. Freezing temperatures may require piping, valves, and tanks to be heat traced and insulated. Intense sun may degrade standard PVC piping and FRP components. UV resistant materials or sun shades should be considered particularly in tropical environments. 

Sometimes the climate works in your favor. The same manufacturer mentioned previously worked with a State Park located in a desert region, where sodium chloride brine was generated as wastewater from ion exchange nitrate removal in drinking water treatment. Rather than implementing a complex discharge or treatment system, the manufacturer devised a practical solution: constructing a lined, shallow lagoon beside the treatment facility to allow natural evaporation of the brine. Twice a year, the residual salt was collected and hauled away, demonstrating a cost-effective approach adapted to the desert environment.

Geography

Plants operating at higher elevations need to consider the efficiency loss of pumps with lower atmospheric pressure. Pumps may need to be upsized at higher elevations to achieve the same flow and pressure as those at sea level. 

For land applications of wastewater or percolation ponds, the ground’s ability to absorb and hold water, and the impact on the water table will be a consideration as to whether this is allowed.

Finally, the seismic zone of the facility and a local wind study should be considered when installing equipment outside. The structural design of the equipment will need to be suitable, and likely signed off by a P.E. as suitable for these factors.

Footprint Availability

An important question to ask when planning a wastewater treatment system is, “Where are we going to put this?”

Water treatment technologies are not created equal in terms of how much space they occupy per unit water treated. Technologies like membranes, ion exchange, media filters, and ElectraMet® electrochemical systems tend to occupy a small amount of space relative to the amount of water they treat.

Technologies that involve chemical reactions, biological digestion, and clarification through settling tend to occupy more space. With these technologies an important design factor is allowing sufficient time for reactions to fully occur, micro-organisms to fully digest waste, or particles to fully settle to the bottom of the tank. If we have a 50 gallon per minute waste stream and a reaction requires 20 minutes, we’re committed to having at least a 1000 gallon reaction tank unit. This value often increases further to add a safety factor in the event of higher flow or longer residence time operations.

The number of unit operations in a treatment process will also affect footprint. Let’s compare physical chemical separation and electrochemical separation as an example. In a physical chemical separation we would typically see 1-3 reaction tank units for flocculation and coagulation, a clarifier for settling, and a post filter sometimes in the form of a sand filter. To manage the settled sludge it is common to have a sludge tank accepting blowdown from the clarifier, and then a filter press to dewater sludge. With electrochemical separation we might expect a single skidded assembly for dissolved metals capture, and a second skid to process the metals into solid tubes.

An important first step when planning your treatment system might be to measure any available space inside and outside the facility. Some technologies perform well outdoors depending on the climate.

If it becomes apparent that additional indoor space will be required, obtaining the cost of building construction should be obtained at the earliest point possible. Building costs will count against indoor only technologies when compared against systems which can be installed outside.

Get In Touch

As we wrap up part 2 of our “How to Plan a Wastewater Treatment System” series, we would encourage engineers to reach out early and often to technology providers, and ask for assistance in understanding their options.

ElectraMet’s team has extensive expertise in electrochemical processes for removing and recovering dissolved metals. If your project involves removing dissolved metals from wastewater, we’re here to help.