April 2014 marked the centenary of the activated sludge process, which was invented by William Lockett and Edward Ardern in Manchester on the 3rd of April 1914. During this time, England was experiencing severe water quality issues as a result of advanced industrial development and increasing populations, with frequent sanitary issues leading to an increased demand for improved water quality.
As a result of this demand, the first Royal Commission on River Pollution and the Royal Commission on Sewage Disposal were established in 1865 and 1898 respectively. The formation of the Royal Commission on Sewage Disposal was a milestone in the development of wastewater treatment technology. This commission evaluated new treatment procedures and also recommended the use of the now obligatory BOD5 testing procedure in 1908. The well recognized effluent standard limits of 30 mg/l TSS and 20 mg/l BOD with full nitrification was adopted later in 1912.
A 1918 Activated Sludge Process Patent application by Walter Jones
These effluent standards proved to be a challenge for the incumbent treatment technologies, which struggled to meet the standards. In their efforts to improve the existing treatment processes, Lockett and Ardern, who were researchers working under Gilbert John Fowler at Manchester Corporation’s River Division at the Davyhulme Laboratories, investigated the aeration of sewage and invented the activated sludge process, as we know it. They presented their breakthrough technology in a paper entitled ‘Experiments on the Oxidation of Sewage Without the Aid of Filters’ in 1914.
Nowadays the activated sludge process is one of the most widely used wastewater treatment processes worldwide. The activated sludge process successfully treats municipal and industrial wastewaters, and it has restored water and river quality on a global scale. The global municipal activated sludge treatment market is estimated to be worth approximately $2.2 billion, whilst the industrial activated sludge market is approximately $1.8 billion.
The activated sludge process has undergone changes in terms of improvements and developments, particularly regarding nutrient removal and dissolved oxygen control. The process’s BOD removal capability has remained the same over the years and it still achieves the effluent standards limits required. However, oxygen demands and overall energy requirements remain the primary disadvantage of the process, as activated sludge can account for up to 60% of the total electrical requirements of the entire WWTP.
With this in mind, there are many new innovative technologies entering the market that are focused on reducing the oxygen consumption and providing an alternative to activated sludge in the near future. One such example would be Oxymem’s Membrane Aerated Biofilm Reactor (MABR) technology, which utilizes a gas permeable membrane to deliver oxygen more efficiently and directly to the microorganisms, reducing the energy consumption. The process is reportedly 4 times more energy efficient than activated sludge. Oxymem’s MABR technology is currently being trialed at a demonstrator unit at Severn Trent Water in Birmingham, and the company will be presenting their MABR technology at this year’s IWA Leading Edge Conference in Abu Dhabi from 26th to the 29th of May. BlueTech Research will also be at the Leading Edge Conference hosting a workshop exploring water technology innovation in the Oil and Gas industry.
Similarly, innovative and more efficient nutrient removal technologies have also entered the market, primarily to provide side stream treatment including technologies such as ANAMMOX and DEMON. The ANAMMOX (anaerobic ammonium oxidation) process for example is a biological process that effectively shortcuts the natural nitrogen cycle. Annamox bacteria convert the ammonium (NH4+) and nitrite (NO2–) into nitrogen gas. In this way the nitrification step (associated with the traditional nitrification stage in activated sludge) is eliminated, thus reducing oxygen requirements and energy costs by approximately 60%. Paques installed the first full-scale ANAMMOX in 2002, and there are currently approximately 20 reference facilities worldwide. Although ANAMMOX has thus far been used as a side-stream treatment, the next step, which could be game changing to the activated sludge market, is the adoption of ANAMMOX for mainstream domestic wastewater treatment.
Microbial encapsulation technologies, such as those offered by LentiKat’s and Microvi Biotech Inc., also improve on the traditional nutrient removal capabilities of the activated sludge process. LentiKat’s biocatalyst technology is a lentil shaped, porous polyvinyl alcohol carrier, which encapsulates cultures of nitrification and denitrification bacteria for wastewater treatment. Notably, LentiKat’s biotechnology can operate on a smaller footprint, have lower associated operational costs than activated sludge nutrient removal, and produce less sludge as a result of bacterial quorum sensing.
The Nereda process developed by TU Delft in cooperation with Royal Haskoning DHV, represents an aerobic granular biomass technology, which operates in batch mode. This sludge has two layers, an aerobic outer layer and an anoxic inner layer. This results in higher biomass concentrations in the same equivalent size of a standard SBR or activated sludge system. Additionally the sludge generated settles faster and generates higher % solids sludge than activated sludge. There are approximately 10 reference facilities globally, and 20 planned facilitates. The technology appears to be in the early adopter section of the technology adoption curve. There seems to be significant merit to this technology in terms of lower energy use, lower footprint, and lower CAPEX and OPEX than traditional activated sludge. The Nereda process is poised to potentially take a significant portion out of the existing MBBR and IFAS markets.
The above examples show that technologies are available to significantly improve upon the traditional activated sludge process, with more efficient alternatives in terms of BOD and nutrient removal rates being rapidly commercialized. While the activated sludge process has served us well, an exciting time lies ahead with so many relatively recent technological advancements to build upon the foundation that it established over the last 100 years.
Photo Credit: John Rostron
