Advanced pre-treatment of stripped biogas slurry by polyaluminum chloride coagulation and biochar adsorption coupled with ceramic membrane filtration

Biogas slurry retention is a critical problem that cannot be solved by using the reuse method. Therefore, a new approach was taken to compensate for the shortcomings in the reuse method. In this study, after ammonia stripping, the ammonia nitrogen concentration in the stripped biogas slurry (SBS) still cannot reach the effluent standard (80 mg/L), so a variety of processes were needed to treat the SBS. Poly-aluminum chloride (PAC) and rice husk biochar (B) were used to pretreat SBS. The effect of different pretreatments on the COD value, ammonia nitrogen concentration, turbidity, total phosphorus (TP), and other indicators was investigated. After different pre-treatments by PAC and biochar, the pretreated SBS was filtered by a ceramic membrane, and the indicators of SBS were removed in the next step. After adding PAC and biochar together, ammonia nitrogen concentration was decreased to 68.09 mg/L, with a removal rate of 63%. The total phosphorus (TP) was also decreased, and its removal rate reached 92.5%. When the SBS was pretreated with PAC and biochar and then filtered through a ceramic membrane under different operating pressures, the removal rates of COD, total nitrogen (TN), turbidity, and suspended solids (SS) reached 81%, 88%, 96%, and 99% respectively. Moreover, by increasing the pressure from 0.1 to 0.3 MPa, the membrane flux was improved from 45 to 100.6 L/m(2).h. This study proves that the combined pre-treatments of PAC and biochar can comprehensively remove various indicators from SBS while ensuring membrane flux during the membrane filtration process. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study focused on different pretreatments of biogas slurry, including using poly-aluminum chloride and rice husk biochar, followed by filtration through a ceramic membrane to remove indicators such as COD, ammonia nitrogen, turbidity, and total phosphorus. The membrane flux was improved by increasing the operating pressure from 0.1 to 0.3 MPa, showing that the combined pre-treatments of PAC and biochar effectively removed various indicators from biogas slurry while maintaining membrane flux.