By Wendy Wert
On October 13, 2009 the American Academy of Environmental Engineers (AAEE) hosted a breakfast and networking event at WEFTEC09 in Orlando, FL. The AAEE/AIDIS/WEF “Trends in Wastewater Treatment” event drew attendees from a broad spectrum of the environmental profession. AAEE President, Debra R. Reinhart Ph.D., P.E., BCEE, welcomed attendees and introduced the featured speaker, James L. Barnard Ph.D., P.E., BCEE. Dr. Barnard is recognized internationally as “the Father of Biological Nutrient Removal (BNR).” A celebrated 40-year career includes groundbreaking work that forms the basis for all BNR process configurations in use today. His current research on membrane and biofilm technology is leading to innovations that may reduce BNR plant size by more than two-thirds.
Dr. Barnard led environmental professionals on an entertaining historical journey through wastewater treatment. His presentation highlighted the discovery of the activated sludge process, major trends in wastewater treatment, drivers for Research and Development, wastewater as a resource, and possible future scenarios.
Dr. Barnard correlates the beginning of the environmental engineering profession with the 1914 Arden and Lockett publication of The Activated Sludge Process. The activated sludge process continued as the, predominate wastewater treatment method into the 1970’s. Then the industry predicted the end of the activated sludge process in favor of newly introduced physical/chemical processes. Successful examples of these are tertiary high lime at Lake Tahoe and ammonia stripping at Pretoria. Other types of physical/chemical processes introduced at this time include chemically enhanced primary treatment (CEPT), ion exchange for ammonia removal, recalcination, and granular activated carbon (GAC). These physical/chemical processes continued to gain popularity until 1975.
In 1975 the Goudkoppies plant in Johannesburg, South Africa was completed. This was the first full-scale plant in the world specifically designed for high-rate biological nitrogen removal without the addition of chemicals. With the inclusion of anaerobic zones (1974), the plant achieved 85% nitrogen removal and 90% phosphorus removal. This triumph marked 60 years of the activated sludge process and renewed the popularity of this process for wastewater treatment applications.
Dr. Barnard then discussed the introduction of fixed growth systems such as moving bed biological reactors (MBBR) and rotating biological contactors (RBC). Denitrification is possible in these systems with the addition of a carbon source such as methanol. Once again Dr. Barnard reported with a smile, that the end of the activated sludge system as the, predominate wastewater treatment technology was forecast.
However, technological advances such as the Integrated Fixed-film Activated Sludge (IFAS) and Membrane Bioreactors (MBR) once again renewed the applicability of the activated sludge process by providing provides for additional biomass within a wastewater treatment facility. Industry practice usually focuses on increasing the bacterial population to meet the system kinetic needs. However, designers often encounter clarifier solids loading limitations that put an upper limit on the amount of biomass that can be carried in the suspended growth system. IFAS systems and MBR’s provide physical mechanisms that support additional bacterial populations in the activated sludge process. Once again the activated sludge process has been revived and coupled with technological advances.
Dr. Barnard then discussed the motivation for technological advances within the field of environmental engineering. These include increased stress to natural resources due to population growth, the need to protect water resources from eutrophication, the need to recover energy, the need to recover resources, the need to reduce endocrine disrupting compounds (EDCs), the need to reduce green house gasses (GHG). Most of these are correlated to the primary driver for advancement, which is our need to meet the needs of an increasing global population with limited global resources.
Not only has the population expanded but the global culture is changing. For example it is predicted that by 2035 60% of the global population will live in cities. The World Watch Institute estimates that in 2007 greater than 50% of the population is urban.
Dr. Barnard then shared an interesting consequence of the stress to the environment. As it turns out, presently the receiving water to the North of Johannesburg is experiencing eutrophication. Ironically, Johannesburg is not using the BNR process that they are famous for pioneering. So how do we as environmental practitioners contribute to the solution of these global issues? Dr. Barnard mentioned the limits of technology (LOT) counterpoint and said that this is a meaningless argument and should not be used. In the absence of limits however, there are some constraints must be considered as we move forward with advanced technological solutions. Viable solutions must be sustainable and economically justifiable.
Responsible stewards will conduct least cost analyses (LCA) studies that include components that address the rationality of regulatory targets (N limits of 2.5 mg/L, P limits of 0.01 mg/L) in light of their impact to the receiving water. For example in inland freshwater, it has been well established that phosphorus leads to algal growth. That said, responsible professionals must design systems that use reliable information to protect resources.
Unaddressed violations damage waterways and send the wrong message to citizens, developers, and neighboring localities. The example of the Occoquan Reservoir in Virginia was given. Up to 85% of the flow to the reservoir comes from water purification plants and in 1986, 60% of all streams in the Occoquan Watershed were classified as high quality. Eutrification has impacted the viability of this resource, in an era when the profession is in possession of the knowledge and technology to mitigate these circumstances.
Dr. Barnard introduced the energy discussion by stating that scientific knowledge is sometimes contradictory, which can inhibit action. To illustrate, in 1968 the scientific community was concerned that we were likely to experience global cooling now in 2009, there is concern for global warming. Irrespective of the path forward, it is good practice to design efficient treatment systems.
Most of the energy used in wastewater treatment plants (WWTP) is required for nitrification. That said, Dr. Barnard suggested that we look at the energy use at WWTPs in the context of other demands in order to appropriately assess the energy use required to protect resources in the context of other energy demands. For example the BNR process requires 40 kilowatt-hours (KWh) per person per year, whereas, a two person household typically consumes 14,000 KWh per person per year and the energy cost to pump water from northern to southern California is 355 KWh per person per year. The protective resource potential of BNR processes may justify the associated energy requirements.
Dr. Barnard then highlighted future resource recovery opportunities, such as urine separation, energy recovery, nutrient recovery, and water reuse. Urine in wastewater contains 80% of the N and 50% of the P yet makes up only 1% of the overall volume of domestic wastewater. Effective separation of grey water (shower, kitchen), yellow water (urine and flushwater), and brown water (faeces and flushwater) could lead to more efficient design of wastewater treatment trains that allow for focused specific treatment for the constituents of concern. Anaerobic digestion of solids coupled with power generation could reduce the energy usage of these systems. End uses such as composting and struvite retrieval could lead to recovery of both N and P for beneficial reuse. Undeniably the most valuable product of WWTP’s is recycled water, which can be used for industrial, agricultural, and even potable applications, such as in Windhoek Namibia where water is precious.
Dr. Barnard concluded by asking if the activated sludge process would be around another 100 years. This is very likely, but with innovations such as MBRs to reduce the footprint, addition of membrane filtration components, coupling with power recovery, nutrient recovery, and water recovery opportunities. One example of technological developments is the use of granular activated sludge in the Anammox (Anaerobic Ammonium Oxidation) process, in Gansbaai South Africa. At this facility influent COD (10,000 ppm) is reduced by 99% (<100 ppm), N (200 ppm) is reduced by 90% (<10 ppm), and dissolved P (25 ppm) is reduced by 96% (<1 ppm). There are currently four full-scale operations.