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. Polyaluminum chloride (PAC) and rice husk biochar (B) were used to pretreat SBS. The effect of different pre-treatments 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/m2·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.

Performance of a novel photobioreactor for nutrient removal from piggery biogas slurry: Operation parameters, microbial diversity and nutrient recovery potential.

Photobioreactor is deemed to be one of limiting factors for the commercial application of wastewater treatment based on microalgae cultivation. In this study, a novel Flat-Plate Continuous Open Photobioreactor (FPCO-PBR) was developed to treat piggery biogas slurry. The operation parameters, microbial stability and nutrient recovery potential of FPCO-PBR were investigated. Results showed that the appropriate influent mode for FPCO-PBR was multi-point or spraying mode. The optimal hydraulic retention time and interval time for biomass harvesting of FPCO-PBR were both 2 d. Nitrogen and phosphorus recovery rate were 30 mg L-1 d-1 and 7 mg L-1 d-1 respectively under optimal operating parameters. Microbial diversity remained relatively stable in FPCO-PBR. Biomass production rate of FPCO-PBR was 0.47 g L-1 d-1 under optimal operating parameters. The revenue generated from biomass was estimated to be 15.06 $ kg-1, which means that treating one ton of wastewater can generate $ 7.08 in revenue.

[Treatment of Piggery Biogas Slurry by Enhanced Biological Contact Oxidation with HN-AD Bacteria].

The conventional pretreatment process for swine wastewater is anaerobic fermentation. This process leads to the formation of high ammonia nitrogen, low carbon, and piggery biogas slurry, which usually results in poor denitrification effect, complicated process flow, and long startup period for the subsequent treatment process. In this study, a novel biological enhanced Biological Contact Oxidation (BCO) process using HN-AD bacteria as microbial inoculants, and PAN activated carbon fiber filler as biofilm carrier was proposed for the treatment of piggery biogas slurry. In the early stage of sludge acclimation, it was found that when NH4+-N concentration was higher than 500 mg·L-1, the nitrification and COD removal in BCO was severely inhibited. When the BCO was enhanced by HN-AD bacteria, however, the tolerance concentration of NH4+-N for bacteria in BCO could reach 600 mg·L-1 and the removal efficiency of NH4+-N, COD, and TN could still remain at a high level. The bio-enhanced BCO process was used to treat the piggery biogas slurry. The average removal rates of NH4+-N, TN, and COD were 86.9%, 70.5%, and 74.4%, respectively, which were higher than the 57.6%, 50.3%, and 50.0% of the traditional treatment process. The concentration of the pollutants mentioned above in the effluent was below the relevant discharge standards. The changes in the microbial community structure during the enrichment process of functional bacteria were studied by high-throughput sequencing technique. The results showed that the dominant bacteria belonging to HN-AD in the biofilm during the sludge acclimation process was Alcaligenes. After the addition of the HN-AD agent, however, the dominant bacteria were Diaphorobacter, Acinetobacter, and Thauer, and the relative abundance of Acinetobacter was much higher than that in the microbial inoculants. The results of scanning electron microscopy further confirmed the existence of bio-enhancement. The surface of the biofilm layer tightly attached to the filler was enriched with rod-like and globular HN-AD functional bacteria.