When considering municipal wastewater treatment upgrades, cast a wide net

Expanding the breadth of available wastewater treatment options to include nontraditional and advanced technologies can net solutions which better match the unique conditions of individual communities and projects. The wide variety of choices available today is fostering innovative thinking in system design that has the potential to increase performance, reduce ongoing maintenance, use or repurpose existing infrastructure, and lower overall construction and ongoing system operation costs.

Capital expenditures for upgrades to publicly owned treatment works, whether due to under-performance, new regulations or simply reaching the end-of-life, are now highly scrutinized by residents, the media, watchdog groups and others. This level of oversight and the limited resources available to cities and towns for infrastructure upgrades may create an atmosphere that limits consideration of the available cost-effective, high-performance options.

Opting for traditional wastewater treatment solutions, which may be more expensive and less versatile, might be the comfort zone. Yet, alternative and advanced technologies frequently offer better performance and greater versatility in challenging environments or where constrained finances are a factor. While there may be a perceived risk related to trying a new approach or technology, most alternative wastewater treatment systems have long, successful performance track records and provide third-party treatment testing and certifications that consistently show superior and reliable treatment capabilities.

Community questions and answers

Too often, community decision makers must maneuver through a minefield of professional advice, existing and impending regulations, voter apathy and tight budget restraints when considering upgrades, expansion or newly proposed wastewater treatment facilities. Distilling the needs of the community and the current situation down to the essentials can help focus the process and may identify options not previously considered.

What are the shortcomings of the existing wastewater treatment program and infrastructure?

Assess the shortcomings of the existing wastewater treatment facilities and infrastructure and the expected potential of future development within the community. Some examples of assessment factors which will impact the decision-making process are:

• A wastewater treatment plant which is projected to, or routinely, receives flows exceeding the rated capacity
• Combined sewer overflows during precipitation events that are exposing the community to scrutiny and the risk of potential penalties
• Watershed proximity issues
• Groundwater pollution including saltwater intrusion for coastal communities and regulatory noncompliance of current facilities or individual residential systems within the community

Is there a plan to sustain healthy community growth and what are the projections that will inform future wastewater treatment needs?

Under-sized or nonexistent wastewater treatment facilities or a lack of an individual wastewater treatment system planning can limit future, desirable development within a community. While each community has a unique set of circumstances and needs, there are commonalities within community sustainability and public health challenges. For example, centralized sewers offer the possibility for large-scale commercial and residential growth, however many communities are more focused on retaining historic and community character. Other communities simply do not have the funds for large infrastructure improvements. Taking a decentralized wastewater treatment approach can enable a community to pursue a phased-in approach to wastewater treatment upgrades that focuses on areas with the most critical need first and expands to the rest of the community over time. 

What is the full range of treatment options available to address the community need?

Broadly, wastewater solutions fall into the following categories: decentralized, centralized or a combination of the two. Communities often hire an independent consultant who specializes in wastewater treatment to assess the situation and make an unbiased recommendation. The top line considerations that will likely be analyzed include anticipated flows, available land, financial considerations, special community characteristics that need to be retained, timeline for treatment upgrades, regulatory guidance or orders, and potential operations and management structure. In such an analysis, community leaders should make clear the desire to consider both traditional and alternative, advanced solutions. Educating residents on the options and costs is also a key step toward garnering community support and funding for a course of action.

What are the short- and long-term costs?

Short-term costs to consider for any new treatment system approach include system design, land acquisition, permitting, legal and construction. Long-term costs include ongoing maintenance, operations, and management, which are often overlooked as a factor when considering options. Also, licensed operators, billing structure, district vehicles such as specialized trucks and specialized equipment are all considerations for the long haul.

Decentralized treatment can offer many cost advantages including smaller design flows, reduced treatment and disposal areas, less regulation related to soil dispersal when compared to heavily regulated single point discharge to a water body, lower energy consumption and reduced ongoing maintenance.

Will the system being considered require professional management?

This is mentioned above but it is a factor that should be fully explored and estimated as part of many new wastewater treatment approaches that are at a scale to handle the anticipated flows to sustain community growth. Often professional management will be mandated by regulatory officials. This is a good thing as it can improve system effectiveness for the long term and provide more extensive monitoring of the system ongoing.

Applications in action

Originally designed in 1959 as a seasonal wastewater treatment facility (WWTF) for a lakeside community in Newbury, N.H., the 50,000-gallon-per-day (GPD) Blodgett Landing Wastewater Treatment Plant was not equipped to meet the treatment requirements of the 21st century. The system consisted of raw effluent pump stations, a 34,000-gallon Imhoff tank, and primary and secondary sand filter/rapid infiltration basins (RIBs). As the population grew and more residences were converted to year-round use, effluent testing and groundwater monitoring confirmed nitrate concentrations were a growing problem.

In 2001, a pilot study was initiated to explore the possibility of collecting a portion of the treated effluent to recirculate through the sludge layer of the Imhoff tank to facilitate denitrification. Recirculation of the “treated effluent” is necessary because the effluent must first be “nitrified” through an aerobic treatment process, which then allows denitrification to occur in an anaerobic environment with a carbon source (sludge) present.

The pilot study was a success and plans were made to incorporate denitrification into the planned upgrade to the treatment plant. However, it was determined that denitrification could be improved if nitrification could be increased in the sand filter aerobic treatment process. Several options were explored before project engineers contacted Presby Environmental Inc. (PEI) for help. PEI recommended incorporating the Enviro-Septic technology into the existing sand filter configuration, which enhances aerobic nitrification and would therefore allow for increased denitrification in the recirculation process. The passive treatment performance of the Enviro-Septic technology using the naturally occurring bacterial process eliminates the introduction of harmful chemicals, biological additives, or additional electrical energy. The subsurface configuration and low maintenance requirements of the system design are desirable attributes for any community. For Newbury, this innovative approach allowed for the rehabilitation and continued use of the existing Imhoff tank and sand filter/RIBs resulting in construction cost savings.

The upgraded Blodgett Landing WWTF has been operating for over nine years with very consistent results. Ultimately, the Enviro-Septic technology allows the Blodgett Landing facility to significantly reduce certain wastewater contaminates including Fecal Coliform, Total Nitrogen (TN), 5-day Biochemical Oxygen Demand (BOD₅) and Total Suspended Solids (TSS).

In Suffolk County, N.Y., nitrogen from residential septic systems is a significant factor in the degradation of Long Island estuaries. When New York State listed portions of the Long Island Sound, Peconic Estuary and South Shore Estuary as impaired water bodies, Suffolk County officials began a review to understand the source of the water supply pollution. Seventy-four percent of Suffolk County uses onsite sewage disposal systems. Currently the drainfield systems in Suffolk County consist of deep leaching pits, cesspools, concrete rings or leaching pools that can be installed as deep as 25 feet. A study revealed numerous pollution sources, however nitrogen pollution from cesspools and septic systems was identified as the primary cause of water quality issues. Impacts include beach closures, toxic algae blooms, and shell fishing restrictions; all detrimental to resident health and tourism revenues.

Sewering was financially unfeasible, so the Suffolk County Health Department initiated the “Reclaim Our Water Initiative” focused on reducing nitrogen by replacing existing septic systems with innovative individual Alternative Onsite Wastewater Treatment System (AOWTS). The initiative includes a demonstration program to pilot these advanced treatment technologies. In this public-private partnership, manufacturers donate the systems including advanced treatment technologies and shallow dispersal drainfields to the demonstration program. Tested and monitored by the County for six months, if the system meets the County “pass criteria” standard of a 50 percent reduction in nitrogen, it gains Provisional Use Approval. The County also upgraded its sanitary code to allow for the changes needed to incorporate these advanced technologies.

Municipalities, states and the federal government have tough decisions to make in addressing wastewater treatment needs and the funds required for infrastructure improvements. New approaches and products provide increasingly better performing, cost-effective alternatives to traditional centralized sewering and older onsite septic system technologies. In many cases, where centralized wastewater infrastructure is not in place or where it is over capacity and no funds are available to undertake new infrastructure projects, taking alternative and/or advanced treatment approaches into consideration is necessary to sustain positive development and to protect waterways, groundwater supplies, public health and the environment.

Dennis F. Hallahan, PE has more than 30 years of experience with onsite wastewater treatment systems’ design and construction. He currently serves as technical director at Infiltrator Water Technologies and is responsible for technology transfer between Infiltrator and the regulatory and design communities. He consults on product research and testing for universities and private consultants. Contact him at [email protected].

Donald Prince, technical advisor, Presby Environmental Inc., holds a Civil Engineering Degree from Vermont Technical College and is a licensed septic system designer and evaluator. He has provided technical support for AES and other Presby Environmental products since 2012. Presby Environmental is an Infiltrator Water Technologies company. Contact him at [email protected].