Enchytraeid Worms and the Bacteria Bed Method Op Sewage Treatment

SUMMARY OF PARTS I AND II The flora and fauna of the bacteria bed of a sewage plant are described, and their interrelationships discussed. A definite cycle in the character and quantity of the Phormidium (Cyanophyceae), the main constituent of the surface growth, is described, the most striking feature of the cycle being the spring off‐loading. The Enchytraeid worm, Lumbricillus lineatus Mull., is briefly described and its habits observed in relation to the conditions in the bed. The worms feed primarily on the growth of Phormidium, and consequently tend to cluster at the surface, when this is abundant and climatic conditions allow. Cold drives them slightly down, but the off‐loading sends them deeply into the bed, when an increased proportion pass out with the effluent. Drying of the surface in summer sends them down in an erratic manner according to the degree of desiccation. The cause of the off‐loading of the surface growth in spring is its change from a leathery to a spongy condition. The worms are mainly responsible for this and, therefore, for the off‐loading. The alga rapidly re‐forms (3–4 weeks) upon the pebbles, worms migrating into it again when it is sufficiently thick. The absence of an off‐loading in summer when the growth is again spongy is attributed to the higher rate of regeneration owing to increased temperature and sunlight, which lessens the effect of the worm depredations. The importance of Lumbricillus lineatus in keeping open a bacteria bed and helping to maintain its efficiency is proved by means of experimental beds. Worms introduced into an inefficient bed with solids rapidly accumulating cleared the medium and allowed active nitrification to commence. If the bed is very badly choked and septic, the worms may be unable to carry out this function. It is probable that all the larger scouring organisms abundant in the bed have this property to a greater or lesser extent. The mechanism of the spring off‐loading is discussed with special reference to the role of L. lineatus in the Leeds bacteria beds. The importance of the maintenance of the biological balance by means of the most economic fauna is pointed out. Finally, the need for more intensive physiological studies is stressed.