Phagotrophic algae can consume bacteria that are the predominant microorganisms present in the waste activated sludge (WAS) generated from municipal wastewater treatment processes. In this study, we developed a combined ultrasonicationphagotrophic algal process for WAS conversion. The ultrasonic pretreatment released small volatile solids (VS) including bacteria from WAS flocs. A phagotrophic alga Ochromonas danica then grew by consuming more than 80% of the released VS, with approximately 30% (w/w) algal cell yield. The process reduced the overall WAS VS by 42.4% in 1 day, comparing very favorably with the 27% reduction in 10 days by aerobic digestion. For stabilizing the solids remaining from the ultrasonic step, the total oxygen uptake required was 65%-92% lower than that for the original WAS, indicating substantially reduced aeration cost. Overall, this novel process enhanced the WAS digestion at lower energy requirements and produced microalgae for other potential uses. © 2021 Water Environment Federation • Practitioner points• At least 80% of released VS from WAS can be processed by phagotrophic algae.• Significant amounts of algae can be produced from WAS.• Ultrasonication-phagotrophic algal process can make sludge management more sustainable.
Sludge management accounts for approximately 60% of the total wastewater treatment plant expenditure and laws for sludge disposal are becoming increasingly stringent, therefore much consideration is required when designing a solids handling process. A membrane thickening aerobic digestion process integrates a controlled aerobic digestion process with pre-thickening waste activated sludge using membrane technology. This process typically features an anoxic tank, an aerated membrane thickener operating in loop with a first-stage digester followed by second-stage digestion. Membrane thickening aerobic digestion processes can handle sludge from any liquid treatment process and is best for facilities obligated to meet low total phosphorus and nitrogen discharge limits. Membrane thickening aerobic digestion processes offer many advantages including: producing a reusable quality permeate with minimal levels of total phosphorus and nitrogen that can be recycled to the head works of a plant, protecting the performance of a biological nutrient removal liquid treatment process without requiring chemical addition, providing reliable thickening up to 4% solids concentration without the use of polymers or attention to decanting, increasing sludge storage capacities in existing tanks, minimizing the footprint of new tanks, reducing disposal costs, and providing Class B stabilization.
A side stream is any process flow resulting from the treatment of biosolids that flows back to the liquid treatment process. Examples of side streams are filtrate or centrate from dewatering operations and supernatant from digestion processes. If a plant recycles very high concentrations of ammonia from side streams, it can be difficult to remove the excess ammonia in the mainstream liquid treatment process making it problematic to comply with effluent discharge limit permit requirements. In fact side stream flows are approximately 1% of the total influent hydraulic plant flow but consequently account for 15% to 40% of the influent total nitrogen load (Pugh and Stinson, 2012). Side stream flows that range from 900 to 1,500 mg/L as nitrogen (N) or more can increase the ammonia concentration in the plant effluent by 3 to 5 mg/L on an average day basis (Phillips, Kobylinski, Barnard, Wallis-Lange, 2006).In addition, side stream flows with excessive ammonia concentrations can create operational issues to liquid treatment process operations, especially to those whose goal is to achieve total nitrogen removal. Excessive ammonia concentration in side streams can cause depletion of carbon to nitrogen ratios since ammonia generally accounts for 60% of the Total Kejldahl Nitrogen (TKN).Reduced carbon to nitrogen ratios can make the denitrification process problematic to achieve. To achieve denitrification when the carbon to nitrogen ratio is depleted in the liquid treatment process adding an external carbon source such as methanol or Micro-C ™ may be necessary, which results in increased sludge loads and operating cost.To improve wastewater treatment plant operations and reduce operating cost associated with the addition of chemicals and disposal costs, treatment of side stream flows can be very advantageous. Side stream treatment can theoretically remove about 85% of ammonia, thereby reducing the load that is returned to the head of the plant. Removing ammonia in side streams requires less volume and lower construction costs than if it were treated in the mainstream liquid treatment process. This is due to the concentrated load and higher temperature which leads to faster kinetics in the side stream. Typically side stream treatment management for ammonia is commonly conducted with biological and physical-chemical processes. Notable sustainable biological side stream management processes include nitrification/denitrification, bioaugmentation, nitritatation and denitritation, and deammonification (ANAMMOX). Typical physical-chemical processes used for side stream management include ammonia stripping (steam, hot air, and vacuum distillation), ion exchange (Ammonia Recovery Process (ARP)), and struvite precipitation (Magnesium Ammonia Phosphate (MAP)). Side stream treatment for ammonia utilizing a biological process while integrating waste activated (WAS) thickening with a membrane unit is a new concept. This paper describes the Digestivore™ process, a new development in side stream treatment technology. This process function...
There are several long term water quality issues associated with discharging nutrients, specifically nitrogen and phosphorus into receiving water streams that are very difficult to manage. Due to these concerns many environmental regulatory agencies have either established nutrient discharge criteria or in the process of developing nutrient management plans. If a wastewater treatment plant is required to meet nutrient discharge limits the design of a sludge digestion system can be very critical especially for facilities that rely on biological nutrient removal (BNR) processes.This paper describes the membrane thickening aerobic digestion process technology that features advanced process control, techniques, and optimization that nearly eliminate nitrogen and phosphorus release in wastewater recycled to the head of the plant thereby protecting the effluent quality of a BNR activated sludge process. A membrane thickening aerobic digestion process offers this distinct advantage in contrast to other common biosolids handling processes without the need for chemical addition.There are up to sixteen operating membrane thickening aerobic digestion processes in the United States with several more in construction. Extensive nutrient data has been collected and evaluated from two existing operating facilities described in this paper then compared against the typical performance of other common biosolids handling processes such as anaerobic digestion, ATAD, aerobic digestion utilizing gravity thickening and decanting. After analyzing and comparing the results of these technologies it can be concluded that membrane thickening aerobic digestion offers the best nutrient management and removal performance in the liquid phase of a biosolids handling process.
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