November 2007, Vol. 19, No.11

Small Communities

20 Years of MBR Performance

Edward A. Clerico

It should be fairly obvious to anyone who has gazed out of a plane while flying across the beautiful open spaces of America that it would be nearly impossible — not to mention undesirable — to spread a spider web of sewer mains over the entirety of this vast rural land to provide centralized sewer systems to every man, woman, and child. Oddly enough, it would seem that this is exactly what the Clean Water Act originally intended by categorizing individual septic systems as temporary solutions that would be replaced as soon as centralized sewers could be provided. It makes one stop and wonder: Did the authors of this original regulation all live in cities and forget about everyone else? Or perhaps they all had septic systems at their own homes and did not want to burden any of their fellow country folk with this same responsibility.

All jesting aside, the issue of decentralized wastewater systems was not on anyone’s mind when the Clean Water Act was drafted, and given the fact that Cleveland’s Cuyahoga River had just been on fire, this lack of concern is quite understandable. The small problems posed by small systems were not on anyone’s radar screen when massive surface water pollution problems were far too numerous. Unfortunately, this initial focus on large-scale solutions for large-scale problems largely ignored the secondary impacts associated with the ensuing development sprawl that would follow behind regional-scale sewer projects.

New Jersey serves as a perfect example of what happens when conventional sewers are expanded into high-growth areas, as was the case throughout the 1970s, 1980s, and 1990s. The myriad water quality and quality of life issues surrounding suburban sprawl became evident as development followed regional sewer expansion. By the early 1980s, it was clear that the central New Jersey area between New York City and Philadelphia would become one continuous sea of development if the brakes were not put on growth.

Government officials from many towns saw two alternatives:

  • Change zoning to prohibit the expansion of regional sewers, and only allow large-lot developments that could accommodate individual wells and septic systems.
  • Devise a new approach whereby small community systems could be configured to allow the combined benefits of better wastewater management together with small-lot cluster development. This option would preserve surrounding open space and offer additional social and environmental benefits, such as reduced impervious surfaces, fewer fertilized lawn areas, and room for wildlife.

The result was a combination of both approaches, as many municipalities faced the conflicting priorities of improving water quality, controlling sprawl, and acting quickly. The impact of the regional sewer expansion is felt for many years as infill development gradually occurs throughout the sewered areas.

With so many people living in such a small area, water quality became a very high priority, and surface and groundwater regulations were subsequently tightened, along with environmental enforcement. New Jersey adopted a zero-tolerance policy toward permit violations while at the same time taking on multiple initiatives to preserve open space. It was during this time of heightened attention to sustainable water quality and enhanced land-use planning that the concept of community onsite wastewater systems evolved. These decentralized wastewater systems were tailored to specific small new communities to allow indirect and direct water reuse without the extension of regional wastewater lines. Such systems were rigorously regulated and carefully planned, and had to meet the highest standard of performance.

Indirect water reuse describes a method whereby high-quality reuse water is utilized to recharge subsurface aquifers that serve as water supply sources for wells and to help maintain base flows in streams. Direct water reuse refers to systems whereby high-quality reuse water is returned for nonpotable supply purposes, usually consisting of toilet flushing, cooling, grounds maintenance, and irrigation. The first of such projects was built in Princeton, N.J., in 1987, and it employed a membrane bioreactor (MBR). Since then, 40 similar systems have been built, mostly in New Jersey, but also in other northeastern states. They serve a wide range of new developments that include single-family and multifamily residential housing, offices, schools, shopping centers, stadiums, public buildings, and commercial business districts. Some systems serve as few as 40 families, and others serve more than 1000 families in addition to associated schools and businesses.

MBRs offered several advantages in such applications and represented the cutting-edge technology to the decentralized wastewater industry long before membrane technology came into vogue for larger municipal systems. Some of the key attributes that were critical to the decentralized applications include

  • the ability to provide high-quality wastewater treatment at all times and thereby comply with strict permit requirements and customer expectations,
  • the adaptability to handle the variable nature of wastewater that is associated with small-scale systems, and
  • the ability to be automated easily so operators could physically operate and maintain systems only periodically while maintaining good continuous process control.

According to Andrew Higgins, chief engineer at Applied Water Management (Hillsborough, N.J.), a company that was at the forefront of the decentralized membrane bioreactor movement in the 1980s, “We have made a lot of progress improving the membrane bioreactors over time, but the basic robust MBR process that uses the modified Ludzack–Ettinger kinetic model remains our workhorse, and the first one which was built 20 years ago gives testimony to their longevity and long-term performance capability.”

Many states have now adopted water reuse standards and are formalizing the water quality aspects of such systems even further. A general overview of the typically required reuse standards is as follows:

  • Turbidity — < 0.5 NTU/95% confidence; never > 5 NTU instantaneous maximum;
  • biochemical oxygen demand — < 10 mg/L;
  • suspended solids — < 10 mg/L;
  • total nitrogen — < 10 mg/L; and
  • total coliform — 1 CFU/100 mL.

As the benefits of decentralized water reuse systems became more widely recognized, their applications have spread throughout the region and now have even moved into urban areas that already include centralized wastewater and water supply systems. In urban areas, such decentralized water reuse systems are mining wastewater from building sewers for nonpotable reuse and are being employed as a means to reduce water consumption, wastewater loading, nutrient loading, and combined sewer overflow discharges on the regional infrastructure. New York City is leading this charge with six such systems already in existence.

During the past 20 years, with numerous successful applications of innovative decentralized small community systems, it has become clear that we will not have to provide centralized sewers to every U.S. citizen and that under certain conditions, expansion of centralized sewers creates undesirable development sprawl. Individual septic systems will continue to play a significant role in the most rural areas, and where their use is inappropriate or undesirable, modern, small-scale community systems — some with direct water reuse and some with indirect groundwater recharge — will fill the gap. And, even more notably, application of decentralized water reuse systems into urban areas now provides a new alternative that can reduce the burden on aging centralized systems struggling to meet the needs of a growing population and its increased water supply and water quality demands. Many of these changes have been and will continue to be driven by MBR technology.

Edward A. Clerico is a water resource consultant and president of Alliance Environmental (Hillsborough, N.J.).

Edward A. Clerico is a water resource consultant and president of Alliance Environmental (Hillsborough, N.J.).