Abstract: A system and method for biological digestion of waste materials in a fluid are provided. The system comprises a tank that is operable in batch mode or in a flow-through mode. A tank and liquid-gas exchanger are provided. Fluid and gas from both the tank and exchanger may be selectively routed and re-routed to desired locations within the system to achieve and optimize aerobic and anaerobic digestion processes occurring within the tank or tanks.

Abstract: A trenching chain arranged with links and pivot pins and with scoop members staggered laterally of the longitudinal direction of the chain and therealong. The scoop members have cup-shaped or curved scoop surfaces which are generally faced in the direction of movement of the chain for scooping earth or the like from the trench. Also, tooth picks or bars are mounted on the chain adjacent the scoop members and extend near the scoop surfaces and are articulated on the chain in a manner different from the movement or articulation of the scoop members themselves, and thus the picks clear the scoop members of dirt or the like when the chain is articulated or moved around a sprocket or the like.