Assessment of free nitrous acid pre-treatment on a mixture of primary sludge and waste activated sludge: Effect of exposure time and concentration

Enhancing sludge biodegradability through free nitrous acid pre-treatment at low exposure time

“…This might be due to the fact that the COD mainly contributing to SMP comes from extracellular polymeric substances and intracellular compounds (non-soluble). Previous studies with FNA observed similar results: the highest increase in the SCOD did not imply the highest increase in the SMP [15,19].…”

“…BMPs were set up with an inoculum to pre-treated WAS ratio of 2.4 on a dry VS basis. Each BMP test contained 80 mg of inoculum and 20 mg of WAS pretreated with FNA (0, 2.49, 3.55 and 4.62 mg N-HNO 2 /L; see Table 1) according to Zahedi et al [19]. Ratios inoculum/ Substrate (I/S) between 2 and 4 are required to ensure the proper performance of BMP tests [20,21].…”

Improving wastewater management using free nitrous acid (FNA)

“…Model analysis suggested the improvement in methane production in AD was due to the sharp increase of hydrolysis rate (from 0.16 to 0.25 d −1 , 50% enhancement) and methane potential (from 201 to 255 L CH4/kg VS added, 27% enhancement). Intensive studies were later carried out to evaluate the FNA pre-treatment with WAS and primary sludge (PS) (Zahedi et al 2016, b, Zahedi et al 2018). Results of some typical studies are presented in Table 4.…”

Effect of free nitrous acid pre-treatment on primary sludge at low exposure times

“…However, in their case a long pre-treatment time (24h) was used as compared with the pre-treatment times used in this study (1-5h). A recent study has also demonstrated that an increase on the FNA pre-treatment time in mixed sludge could result in a reduction on the methane reduction potential (Zahedi et al, 2016). Therefore, it is important to use low pre-treatment times when treating PS with FNA.…”