An A2O process is operated with a 12 d SRT and achieves an effluent soluble P concentration of 0.5 mg/L, and effluent NO3-N concentration of 5.0 mg/L. The internal and return activated sludge (RAS) recycle ratios are 3.0 and 0.5 respectively. Determine: a) The change in effluent soluble phosphorus and NO3-N concentrations if the internal recycle ratio is changed to 2.8 and RAS ratio is increased to 1.0. (10 pts) b) How much additional rbCOD is consumed by nitrate fed to the anaerobic zone

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol