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Oxygenation Tank - Clarifier Design Integration
Published in J. R. McWhirter, Richard Prober, The Use of High-purity Oxygen in the Activated Sludge Process, 2019
The MLSS (or MLVSS) concentration that can be maintained in an activated sludge system is described by Equation 3. As shown, the MLSS concentration depends upon the settling characteristics of the biomass, the clarifier overflow rate, and the recycle ratio. The maximum acceptable design MLSS concentration is dictated in most cases by system economics (i.e., large clarifiers) rather than process considerations. Low design MLSS concentration will reduce the clarifier area but increase oxygenation tank volume also resulting in overall unfavorable economics. In addition, low MLSS concentrations may result in dispersed floc and poor effluent suspended solids levels. Design MLSS and MLVSS concentrations typically range from 5,000 to 8,000 and 3,500 to 6,000 mg/l, respectively, in oxygen-activated sludge systems.
Solids
Published in Barbara A. Hauser, Practical Manual of Wastewater Chemistry, 2018
The Mixed Liquor is a suspended floc mass, and includes not only bacteria, bu also the adsorbed solids from the wastewater, as they are being digested by the bacteria. The Mixed Liquor Suspended Solids (MLSS) concentration is controllable by varying the RAS and WAS pumping rates, and this concentration will determine aeration rate, F/M ratio, sludge age & MCRT. Human control over the biomass concentration is a major advantage of operating an activated sludge treatment plant Volatile and Fixed percentages of the mixed liquor are used to determine biologica efficiency and potential for waste removal.
Activated sludge
Published in Nick F. Gray, Water Science and Technology: An Introduction, 2017
The concentration of suspended solids in the aeration tank, commonly known as the mixed liquor suspended solids (MLSS) concentration, is a crude measure of the biomass available for substrate removal. It is measured by filtering a known volume of mixed liquor through a Whatman GF/C pre-weighed filter paper which is then dried at 105°C. The increase in weight is used to assess the dry solids concentration of the mixed liquor and is expressed in either mg L−1 or gm−3. It is the most basic operational parameter and is used to calculate other important operating parameters including sludge production. A significant portion of the MLSS can be inorganic, so by burning the dried sludge at 500°C in a muffle furnace, the MLSS can be expressed as the mixed liquor volatile suspended solids (MLVSS) which is a more accurate assessment of the organic fraction and hence of the microbial biomass. However, neither the MLSS nor the MLVSS can distinguish between the active and non-active microbial fractions, or the level of sludge activity. Other methods must be used if an accurate estimation of microbial activity is required (e.g. biochemical assessment), although for routine operational control, the MLSS is sufficient. The normal MLSS range is 1500–3500 mg L−1 for conventional activated sludge units, rising to 8000 mg L−1 for high-rate systems (Table 11.2). The MLSS concentration is controlled by altering the sludge wastage rate. In theory, the higher the MLSS concentration in the aeration tank, the greater the efficiency of the process as there is a greater biomass to utilize the available substrate. However, in practice, high operating values of MLSS are limited by the availability of oxygen in the aeration tank and the ability of the sedimentation unit to separate and recycle activated sludge.
The design for wastewater treatment plant (WWTP) with GPS X modelling
Published in Cogent Engineering, 2020
The combined process oxidizes a high proportion of the influent organics relative to the NH3-N concentration. In combined carbon oxidation-nitrification processes the ratio of BOD (biological oxygen demand) to TKN is greater than 5, whereas in separate processes the BOD to TKN ratio in the second stage is greater than 1 and less than 3. Total Kjeldahl Nitrogen (TKN) is a parameter used to measure organic nitrogen and ammonia. The TKN content of influent municipal wastewater is characteristically between 35 and 60 mg/L. TKN is a regular parameter that indicated the total concentration of organic nitrogen and ammonia. The ratio of BOD5 to TKN can be used as an indicator for efficiency of removal nitrogen and providing useful information in the rate of biodegradability in WWTP design. The term MLSS means (Mixed liquor suspended solids) is the concentration of suspended solids, in an aeration tank during the activated sludge process, which occurs during the treatment of waste water. The F/M ratio is a measure of the amount of food, or BOD, that is given to the microorganisms in the aeration tank. Additionally, MLVSS is defined as mixed liquor volatile suspended solids. MVLSS is generally defined as the microbiological suspension in the aeration tank of an activated-sludge biological wastewater treatment plant or it is represented the concentration of biomass in the activated sludge. The MLVSS is calculated as shown in Table 9. The hydraulic retention time (HRT) in wastewater treatment plant is a measure at an average length of time holding the wastewater in a tank. In addition, the biomass yield is defined as the ratio of the amount of biomass produced to the amount of substrate consumed (g biomass/g substrate). Moreover, in most aeration treatment systems, it is necessary to calculate the detention time is necessary in order for the microorganisms in the aeration system to absorb, adsorb and remove the contaminants (bacteria food) in the wastewater. Other calculations like sludge age, sludge produce and sludge produce in term of TTS are explained in Table 9 as a part of the calculations of the design of aeration tank.