Effect of organic components and aeration regimes on the efficiency of a multi-soil-layering system for domestic wastewater treatment

Multi-soil-layering (MSL) system can be applied to wastewater treatment. The component of an MSL system can be varied as a function of site-specific availability of materials. This study investigates the comparative efficiency of five MSL systems as a function of alternative organic materials (Japanese sawdust, Thai sawdust, rice straw, kenaf, and corncob). The MSL systems were set up in 15 X 50 X 100 cm boxes consisting of "soil mixture blocks" alternated with a zeolite layer. The February-May 1999 results indicated that all the MSL systems under a non-aeration regime effectively reduced the biochemical oxygen demand (BOD5) and removed soluble reactive phosphorus (SRP) with percentages ranging from 88.0-99.8 and 92.5-100, respectively. From January to September 2000 when an on-off aeration regime was adopted, the MSL treatments comprising rice straw, kenaf, and corncob continued to effectively reduce BOD5 and remove SRP. On the other hand, the efficiency of Japanese sawdust and Thai sawdust MSL treatments in reducing BOD5 and removing SRP gradually decreased. Fine particles and slowly decomposable characteristics of Thai sawdust and Japanese sawdust induced compaction and subsequent clogging. Therefore, rice straw, kenaf, and corncob were found to be more appropriate than Thai sawdust and Japanese sawdust for use as components of the MSL systems. Aeration at a rate of 64,000 L m(-3) d(-1) for 1 week enhanced BOD5 reduction and SRP removal, especially, when clogging was observed. However, aeration at this rate reduced the TN removal efficiency of the MSL system due to the inhibition of denitrification, excessive nitrification as well as the discharge of stored NH4+-N.