Hydrolysis Combined with Chemically Enhanced Primary Treatment to Remove COD and Retain Nitrogen in Sewage

In autotrophic nitrogen removal, heterotrophic denitrifiers compete for nitrite/nitrate with autotrophic denitrifiers in the presence of organic matter, leading to a decline in autotrophic denitrifiers. In this study, a combined process of hydrolysis and chemically enhanced primary treatment (CEPT) was used for sewage pretreatment that removed chemical oxygen demand (COD) but reserved total nitrogen (TN). When raw water was hydrolyzed for $19\min$, approximately 19% of TN was converted to ${\mathrm{NH}}_4^{+}─\mathrm{N}$ and amino acid in the hydrolysate, resulting in ${\mathrm{NH}}_4^{+}─\mathrm{N}$ and amino acid accounting for about 75% of TN in raw water. When ${\mathrm{FeCl}}_3$ and bioflocculant were added into the hydrolysate at a final concentration of 40 and $10\mathrm{mg}/\mathrm{L}$, respectively, approximately 70% of COD and approximately 89% of total phosphorus (TP) were removed from the hydrolysate. Finally, approximately 80% of TN in raw water was reserved primarily in the form of ${\mathrm{NH}}_4^{+}─\mathrm{N}$ and amino acid ($>90\%$), which could be directly or indirectly used for autotrophic nitrogen removal. Combination of bioflocculant and ${\mathrm{FeCl}}_3$ can save 9% of the cost when removes $1\mathrm{g}$ COD from sewage.