What is MLVSS?
MVLSS is commonly defined as a microbial suspension in an aeration tank of a biological sewage treatment plant containing activated sludge.
Biomass solids in biological wastewater reactors are usually reported as total suspended solids (TSS) and volatile suspended solids (VSS). Solid mixtures resulting from the combination of recycled sludge and wastewater flowing into the bioreactor are called mixed suspended solids (MLSS) and mixed liquid volatile suspended solids (MLVSS).
The solids are composed of biomass, non-biodegradable volatile suspended solids (nbVSS), and totally inert inorganic suspended solids (iTSS).
What does the MLSS test measure?
The MLSS test measures the total concentration of suspended (insoluble) solids in the mixture in the activated sludge tank of the activated sludge system. Suspended solids (MLSS) in the mixture is important for determining system performance and solids inventory and is used to determine when to dispose or recycle sludge.
To test suspended solids (MLSS) in a mixture, a well-mixed sample must be filtered through a standard weighing glass fibre filter. The residue remaining on the filter is dried to a constant temperature at temperatures between 103 ° C and 105 ° C. The weight increase of the filter represents the total amount of suspended solids in the sample.
Underwater aggregates of non-uniform material from large, suspended particles or samples can be excluded from total suspended solid measurements if their inclusion is determined not to represent the entire sample. The sampling range should also be limited to a size that does not produce a residue of more than 200 mg.
What do high levels of MLVSS represent?
High levels of suspended solids (MLVSS) in wastewater are associated with the formation of excess solids due to increased BOD (Biochemical Oxygen Demand) loading, and of biomass such as undernourishment and bulky sludge. It may indicate a problem.
High MLSS values ??can also be due to high flow rates or inadequate settling times. After measuring the suspended solids value of the mixture, a test of suspended solids (MLVSS) in the mixture can be performed to measure the concentration of suspended solids in the aeration tank of the activated sludge system. Data on volatile suspended solids in the mixture are important for determining system performance and biological inventory. The filter used for suspended solids testing (MLSS) in a mixture is ignited at 550 ° C for 30 minutes. The weight loss due to the burning of solids represents the volatile solids in the sample.
How to calculate biomass in MLVSS?
This formula will establish the MLVSS of a sewer wastewater treatment plant:
MLVSS = (Primary effluent BOD or COD * Flow) / Desired F/M ratio
Let us understand this with the help of an example:
Calculate biomass of MLVSS from the following data;
Soluble substrate concentration So= 192 BOD or bsCOD g/m3
Flow = 4.0 MGD
F/M ratio = 0.3 COD, lb./MLVSS,
MLVSS = (192* 4 *8.34)/0.3= 21248 lb.