Drying Technology
According to Frost & Sullivan, the decentralized containerized/packaged water and wastewater treatment (W&WWT) systems market is estimated to garner $7.92 billion in revenue by 2026 from $5.22 billion in 2020, an uptick at a 7.2 percent compound annual growth rate.1 Rising water stress worldwide is compelling authorities in charge of water and sanitation globally to explore decentralized solutions, pushing the demand for decentralized containerized/ packaged W&WWT systems and ensuring water sustainability and circular economy.
For most mid-market community, education, commercial, and food facilities, it is commonly assumed that the wastewater generated by the operation will be handled by the local municipal wastewater treatment plant (WWTP). It’s rather simple: Discharge wastewater generated by the operation down the drain, which is transported down septic lines, sometimes for miles and miles, until received by the WWTP, where it is treated. Pay a sewer bill and let someone else deal with the waste.
In the past, discharging wastewater to a municipal WWTP may have been the only practical solution for managing and disposing of wastewater. Today, mid-market and even large facilities may want to consider opportunities to reduce costs, energy, and water consumption and improve the sustainability of their operation with decentralized wastewater treatment systems (DEWATS) installed onsite.
Improve Sustainability By Reducing Water And Energy Consumption
DEWATS are installed and operated onsite, at the source of wastewater, and eliminate the need to discharge wastewater offsite and pay a sewer discharge bill. Eliminating the sewer bill, by itself, can correlate to a significant savings. A mid-market food processor in the Midwest discharging 500,000 GPD of food cleaning wastewater may pay an annual sewer bill over $1 million.
The composition of wastewater is 99.9 percent water and the remaining 0.1 percent is what is removed. A DEWATS installed onsite at the above food processor could recover that water as clean water used for cooling tower makeup and cleaning food processing equipment, saving 180 million gallons of water annually.
Let's say a mid-market commercial development project involves an office building (750,000 sq. ft.), hotel (400 rooms), retail space (350,000 sq. ft.), and two restaurants netting a daily wastewater flow of 240,000 GPD. At a sewer discharge rate of $5 per thousand gallons, and a potable water supply cost of $5 per thousand gallons, the annual cost of wastewater treatment services plus the corresponding water supply cost would be $876,000. Total annual water consumption would be 87.6 million gallons. If the wastewater were treated onsite, it would produce clean, National Pollutant Discharge Elimination System (NPDES)-permittable effluent — over 80 million gallons per year — that could be reused onsite for cooling tower makeup, irrigation, and a variety of other non-potable graywater uses.
Some modern membrane bioreactors (MBRs) significantly reduce energy consumption for wastewater treatment by operating at a low dissolved-oxygen (DO) set point, thereby minimizing aeration energy, which is the largest energy-consuming activity in wastewater treatment. In the facultative membrane bioreactor (FMBR) pilot demonstration summarized below, the FMBR reduced electric energy consumption by 77 percent for wastewater treatment processes.
Reduce Infrastructure Costs And Bottlenecks
When DEWATS is installed upstream at the source of wastewater, eliminating discharge to the municipal wastewater treatment plant, the WWTP gains the corresponding flow of wastewater as increased capacity. In the above development example, 87 million gallons of wastewater per year would not be discharged to the municipal wastewater treatment plant. The WWTP gains the equivalent in additional treatment capacity to support economic development and new customers, eliminating or at least delaying expensive plant upgrades and expansions. This helps keep rates down for wastewater treatment services provided by the local municipal WWTP. This also may enable economic development to move more quickly when facing capacity limitations of the local municipal WWTP.
The Facultative Membrane Bioreactor
FMBR is a modern, low-energy, small-footprint MBR wastewater treatment technology that provides a single-tank solution for onsite wastewater collection and treatment. The FMBR produces clean water effluent that can be reused onsite, while generating a minimum volume of sludge requiring further processing or offsite disposal. It is suitable for handling the wastewater treatment needs of commercial, retail, hospitality, educational, healthcare, and community facilities and activities, and wastewater treatment plant upgrades and expansions.
The FMBR Pilot Demonstration Project
The first FMBR pilot demonstration project installed in the U.S. was in November 2019 at the Plymouth, MA, Municipal Airport. This was made possible by winning a global competition hosted by the Massachusetts Clean Energy Center (MASSCEC) for wastewater treatment innovations that minimize energy consumption. It was granted the highest available funding of $150,000.
Requirements
1. Replace a sequencing batch reactor (SBR) wastewater treatment process due to high energy costs.
2. Treat 5,000 GPD of wastewater generated by the airport and surrounding restaurants.
3. Meet effluent discharge permit requirements:
3.1 Biological oxygen demand (BOD) < 30 mg/L
3.2 Total nitrogen (TN) < 10 mgN/L
3.3 Total suspended solids (TSS) < 30 mg/L
Carbon, Nitrogen, And Phosphorus Removal
Daily testing of influent and effluent for TN, phosphorus (P), BOD, and TSS showed strong performance of carbon (C), TN, and P removal. Over one year of operation, the FMBR pilot observed average daily P removal of 10.0 mgP/L to <1.0 mgP/L; TN removal of 62.7 mgN/L to 4.1 mgN/L; BOD removal of 371 mg/L to non-detect; and TSS removal of 79 mg/L to non-detect.
Key Benefits Observed
~77% energy savings
Electric energy savings averaged 77 percent from February to December, 2020, and a 73 percent reduction in energy cost.
~65% less biosolids volume requiring offsite disposal
The volume of residual biosolids requiring offsite disposal was reduced 65 percent, from 20,000 to 6,500 gallons per year.
~75%+ reduction in footprint
The footprint of the wastewater treatment system was reduced by more than 75 percent. The SBR was installed in 2003 with a design flow capacity of 25,000 GPD. The footprint is 2,303 sq. ft. The actual flow of wastewater requiring treatment at the airport is 5,000 GPD. Therefore, the FMBR pilot design flow capacity is 5,000 GPD. The footprint is 224 sq. ft. This correlates to a 90 percent smaller footprint than the SBR system that it replaced. If the FMBR had a design flow capacity of 25,000 GPD, the footprint would be approximately 500 sq. ft. This correlates to a 75 percent reduction in footprint as compared to the legacy SBR.
30-day installation
The FMBR equipment arrived at the site on Oct. 25, 2019. The installation was completed on Nov. 7. The operation started on Nov. 12. The effluent began meeting the discharge permit stably on Nov. 25.
FMBR — How Does It Work?
Removal of nitrogen
The FMBR completes nitrification/denitrification in one step, simultaneously, in a low-dissolved-oxygen condition (<0.5 mg/L). The nitrification/denitrification process is enhanced by encouraging a facultative environment and maintaining a high activated sludge concentration. A facultative environment is encouraged by carefully controlling DO, the gradient of DO distribution, and the liquid flow regime in specialized control schemes that are designed to optimize nitrogen removal.
Removal of organic matter
The FMBR is designed to decompose organic matter to a greater degree than traditional MBR or SBR wastewater treatment processes. This is accomplished by facilitating a higher-than-normal concentration of facultative heterotrophic bacteria that decompose organic matter. A higher concentration of this bacteria is achieved by maintaining a higher-than-normal activated sludge concentration in the FMBR reactor.
Removal of phosphorus
By decomposing organic matter to a greater degree than normal, the FMBR is designed to generate a greater amount of volatile fatty acids (VFAs). This means more food for polyphosphate-accumulating organisms (PAOs). The unique operating characteristics of the FMBR are designed to enable biological phosphorus removal in the same single reactor where simultaneous nitrification/denitrification (SND) occurs, when the proportion of each component in the influent is appropriate.
Reduction of organic residual sludge (biosolids)
The FMBR is designed to significantly reduce residual biosolids mainly on two aspects. First, many anaerobic or facultative anaerobic bacteria with low productive rate coefficients are enriched in the facultative environment. This results in a low sludge productive rate, while meeting the requirement of carbon, nitrogen, and phosphorus degradation. Second, the sludge loading of the FMBR system is low and the sludge age is long. As a result, biological nutrient removal (BNR) microbes are basically in the endogenous respiration period, and the sludge growth rate and decomposition rate are basically balanced. The benefits are a very small production of biosolids requiring offsite disposal and a much longer amount of time between offsite disposal occurrences than traditional processes.
FMBR — How Is It Different?
Traditional SBRs perform nitrification/denitrification in two steps with a DO concentration commonly >1.0 mg/L and remove phosphorus in a separate biological process. Some modern MBR systems complete nitrification/denitrification simultaneously, in a low DO condition, saving energy and footprint. Normally, however, phosphorus is removed in a different process. With the FMBR, phosphorus is removed biologically in the same reactor and ecological system where simultaneous nitrification/denitrification occurs, further reducing footprint and cost.
How Does The FMBR Save Energy, Residual Biosolids, And Footprint?
16S DNA sequencing confirmed the FMBR pilot system was mainly relying on SND bacteria to remove nitrogen.2 SND requires 20 to 30 percent less oxygen and 40 percent less carbon than most other nitrogen bacteria. This translated into a 77 percent energy savings. A high abundance of denitrifying phosphate accumulating organisms (DPAOs) was also observed, specifically Tetrasphaera.3,4 The high abundance of SND and DPAO bacteria, which have stronger endogenous respiration, reduced sludge production by 50 percent.5 Combined with other factors, annual biosolids volume requiring offsite disposal was reduced by 65 percent. In the end, the DNA and operational data confirmed the results — simultaneous removal of C, N, and P, in a single tank, with a surprisingly small amount of energy, footprint, and biosolids waste.
Takeaway
Treating the wastewater generated by your facilities or the facilities that you service, onsite at the source, may not have been even a consideration in the past. If you are seeking new ways to conserve and reuse water at mid-market community, education, commercial, and food facilities or evaluating wastewater treatment and water reuse options for a new facility, expansion, or development, modern DEWATS like the facultative membrane bioreactor may be worth looking into. You may not only improve the financial performance of the operation but also inspire the people who work and live in the area by setting the example with action toward a more sustainable future.
