Nutrients release and phosphorus distribution during oligochaetes predation on activated sludge

Abstract

a b s t r a c tRelease of nitrogen and phosphorus into effluent of activated sludge process was reported in the recent researches of sludge reduction induced by oligochaetes. In this study, batch test and radioisotope 32 P tracer test were therefore carried out to further investigate nutrients release and phosphorus distribution among supernatant, sludge and worm during predation of oligochaetes on sludge. Results showed that more nutrients release into supernatant occurred in the tests of worms with sterilized sludge than that of worms with activated sludge, and release of nitrogen and phosphorus was few in the tests of worms with activated sludge. Statistical analysis showed that no factor was significantly correlated with phosphorus concentration in the supernatant, but time and worm were only two factors significantly affecting total nitrogen (TN) concentration in the supernatant in the test of worms with activated sludge. Through test of radioisotope 32 P tracer, 32 P mainly distributed in activated sludge and supernatant, and more release of 32 P into the supernatant occurred in the test of sludge with worms. After 24 h, 32 P concentration of supernatant in the test of sludge with worms was 9% higher than that in the test of sludge without worms, and 32 P concentration of worm increased by 2.7%. Additionally, the release rate of phosphorus into supernatant caused by worm's predation on activated sludge was 0.1211 mgTP/gWorm (wet weight) h.

Aquatic worms eat sludge: Mass balances and processing of worm faeces

“…Sludge is passed over the worm reactor at a certain flow rate, resulting in the return of a mixture of non-consumed sludge, worm faeces and released metabolites to the WWTP. Metabolites released by the worms can therefore be converted already by the sludge present in the worm reactor [10], e.g. the conversion of released ammonia into nitrate.…”

A comparative study of synchronous treatment of sewage and sludge by two vermifiltrations using an epigeic earthworm Eisenia fetida

“…Concerning on predation on bacteria to minimize sludge reduction in biological wastewater treatment, a variety of researches mainly focus on the predation by protozoa and metozoa in activated sludge system [1,2,6,7], while vermifiltration utilizes a higher and larger oligochaete organism-earthworms in an attached-carrier biofilm reactor to acquire low sludge production. The former reported on the sludge yields of a pilot scale activated sludge system for domestic wastewater treatment ranged from 0.15 to 0.17 kg SS/kgCOD removed at ambient temperature of 18-23 • C, and that of the submerged MBR was in the range of 0.00-0.15 kg SS/kgCOD removed at the temperature of 20 • C [9,17].…”

“…An ideal way to solve sludge-associated problems is to reduce sludge production in the wastewater purification process rather than the post-treatment of the sludge generated [5]. There is therefore a growing interest on sludge reduction by predation on bacteria [1,2,6,7], which is based on the ecological principle that during energy transfer from bacteria to higher trophic level organisms (protozoa and metazoa), energy is lost due to inefficient biomass conversion. Thus the predator may make a large contribution to biomass reduction [8].…”

“…Thus the predator may make a large contribution to biomass reduction [8]. The performance of oligochaetes for sludge reduction in biological wastewater treatment has been paid more attentions than that of protozoa for sludge reduction [1,2,6,7,9]. The oligochaetes used for treatment of excess activated sludge can be divided into two groups, firstly, the large aquatic worms such as the Tubificidae, Lumbriculidae and the semi-aquatic or terrestrial Enchytraeidae and, secondly, the small aquatic worms such as Naidids and Aeolosomatids [4].…”

“…Sewage sludge treatment and disposal is, therefore, becoming one of the most serious challenges in WWTPs 1 as a result of legal constraints, rising costs and public sensitivity [2]. It should be realized that biomass production is an important economic factor because the sludge generated is a secondary waste that must be disposed in an environmentally sound and cost-effective manner.…”