Alternate: Sustainable Sludge Management by Control of Microbial Population Dynamics

SUSTAINABLE SLUDGE MANAGEMENT BY CONTROL OF MICROBIAL POPULATION DYNAMICS Rob Whiteman, Ph.D. Technical Director, ABS Inc. For 100+ years engineering technology has employed capital intensive processes for biological wastewater treatment (WWT) using the approach of in-situ growth to control the development of biology under aeration, to flocculate in the clarifier to meet Water Quality Standards. Issues of filamentous bulking and poor settleability result in less concentrated biosolids meaning larger volumes to handle along with poor dewatering characteristics meaning more polymer and expense for dewatering. The increased use of cleaners, antibiotics and hand sanitizers has led to deterioration in the microbial populations for good floc structure and settleability, while reducing viability. The handling and disposal of these biosolids residuals represents a significant cost to Utilities, which employ a range of equipment to reduce the volume and mass: digesters, presses, pelletization or incineration. With increasing environmental pressures for sustainable disposal methods driven there is a need for innovative 'point source reduction' (PSR) technologies and a method or process which improves settleability, allowing an increase in the mean cell residence time (MCRT), hence reduction in wastage and new ways to meet Class A pathogen reduction standards inexpensively. However, now with the discovery of microplastics in drinking water and biosolids, there is even greater demand for a point source reduction technology. Advances in biotechnology and understanding the role of microbial population dynamics in wastewater treatment have led to the investigation of PSR technology, a new approach using an ex-situ growth process to grow and routinely inject probiotics which controls the biology in the treatment system. This resulted in unprecedented beneficial results discovered over the past decade, which improved settleability allowing an increase in the mean cell residence time (MCRT) and hence reduction in wastage. With this reduction in biosolids residual, it was possible to extend the holding times to further reduce the mass of biosolids while improving the quality to make a Class A biosolids residual and in some cases Class AA, which is a breakthrough providing a sustainable, low-cost, affordable method of treatment and disposal. Side Stream Reactor: Biofermentation is a process and method for growing single cell microorganisms in a standalone side stream reactor. The process allows cultivation of specific microbes which are injected from the side stream reactor and have not been exposed to the selection pressures experienced by the wastewater treatment plant. The cultures are grown overnight and injected daily as a 'probiotic' allowing complete control of the microbial population for the first time in 115 years, since development of activated sludge in 1910. Improving Settleability: Settleability is the limiting factor for environmental engineers designing smaller, more compact activated sludge systems. Filamentous bulking is a common occurrence in municipal wastewater treatment, which causes poor settleability by bridging and preventing water escaping from between the flocs as the sludge concentrates in the clarifier. Several of these microorganisms are often associated with high loads of fats, oils and grease, such as Microthrix parvicella and others with long MCRT's of greater than 20 days, such as 0041 and 0675. While the concept of ageing was supposed to encourage flocculation, few systems can operate beyond 25 days without experiencing bulking. Through the introduction of selected microbes using the Biofermentation process, it has been possible to improve settleability substantially allowing the mixed liquor suspended solids (MLSS) to be increased by increasing the MCRT. . The process has been applied at one plant for 3.5 years during which time the MLSS has been raised from 3-4,000 to 9-10,000 with improved settleability and clarity. The improvement in floc structure is seen in Figure 1, while the settleometers are shown in Figure 2. This extended aeration plant now operates with an estimated MCRT in excess of 70 days. REDUCING BIOSOLIDS PRODUCTION: With the ability to improve settleability and hence increase MCRT comes less mass wasted. In part of another 5 year 'Cause and Effect Study', the biosolids production versus food to microorganism ratio (F:M) was compared as shown in Figure 3. The data shows a reduction in the amount of biosolids produced irrespective of F:M when treated with the probiotics. More importantly the R2 in the untreated is only 0.458, while 0.968 in the treated, which demonstrates a more stable, predictable biomass. Overall, the process showed typically a 60+% reduction in biosolids production in the aeration basin. Reducing biosolids production by this amount significantly reduces downstream handling and processing not to mention disposal. 'ADVANCED DIGESTION': Advanced digestion was used which involved injecting probiotics, which compensate for the long MCRT. Figure 4 shows the results in the lbs of biosolids produced per lb of BOD reduced over 10+ years comparing hauling to a chemical process (BCR) and probiotics with and without Advanced Digestion. When only using probiotics in the wastewater treatment system there is a 54-70% reduction in the amount of biosolids produced depending on whether comparing hauling or the chemical process. When coupled with the Advanced Digestion process this plant has experienced in excess of 90% reduction with no biosolids hauled from the facility since April 2017 through 2022. The digester was allowed to digest biosolids without addition of new biosolids for over 60-days. A geometric mean for fecals was taken, which showed that the biosolids met Class A standards (See Figure 5). Metals were also measured which indicate the residuals meet a Class AA under Florida Law. Mass reduction occurred as previously discussed, which is more paramount with new legislation on microplastics and other biosolids contaminants. This facility continues to lead the way in using Biotechnology to resolve biological challenges. In summary, the addition of probiotics has now been proven and even validated with respect to improving settleability by control of population dynamics, providing the operator more control to increase MCRT, while reducing biosolids production 60% economically. This has the ensuing benefits of opening up space downstream for Advanced Digestion, which further reduces biosolids production of up to 90% with the potential to create a Class A or AA residual or economically dispose of the final biosolids because of the substantial reduction in mass and volume.