Water Treatment after Biogas Processing

Pig farm  wastewater ​after biogas ​processing ​is currently ​being treated ​with anaerobic ​decomposition ​tunnels (tunnel ​biogas) in ​Vietnam.  ​ The concentration ​of ​environmental ​pollutants (TSS,​ COD, BOD, ​total N, total ​P) is still ​very high after ​this process ​and before ​wastewater is ​discharged into ​the near by field,​ it needs to be ​treated again.​  ​ How can we ​improve ​pig farm wastewater ​treatment process after biogas ​processing?​  ​