Chemical and biological characteristics of an aerobically digested and three anaerobically digested sewage sludges from metropolitan Syracuse, N.Y. were analyzed. The aerobic digest had a higher organic fraction (ash 39%, carbohydrate 14%), more nitrogen (total N 4.2%), and more phosphorus (total P 1.71%) than the three anaerobic digests (ash 61–80%, carbohydrate 4–6%, total N 0.6–1.3%, and total P 0.75–1.71%). Potassium concentrations were low, and heavy metals varied among sludges.In the two sludges taken directly from centrifuges, nematode density was low which contrasted to the high density of nematodes in sludge from drying beds. Enchytraeidae were found only in the aerobically digested sludge.These sludges were applied separately onto pulverized soil (Teel silt loam) in randomized plots within a glasshouse. Samples were taken at intervals for 260 days and analyzed for chemical and biological components. Rates of change in ash, carbohydrate, total N, and total P were proportional to the original magnitude of these parameters, highest rates being exhibited by samples from plots amended with the aerobic digest; the aerobic digest lost 48% of its organic content in 162 days. Few significant changes over time were noted in available P, CEC, Cu, Zn, and K for a given plot type.The earthworm Eisenia foetida was placed in the plots after 90 days since earlier experiments had shown that two of the fresh anaerobic sludges killed the worms. Earthworms were thriving 170 days after introduction.There were no significant differences between plot types for catalase, peroxidase, or tyrosinase because of high intraplot variation. Total and viable bacterial populations were higher in the sludge amended plots than in arable soils, and declined with time. Mite and collembola populations were low in the sludge‐amended soil but similar to populations in arable soils. Those plots, which were amended with sludges originally deficient in nematodes, showed a rapid increase in these worms, which were bacterial feeders and predominantly Rhabditidae. Enchytraeids increased in all sludge‐amended plots at a slower rate than the nematodes.The plots converged over time with respect to biological and chemical characteristics.
Decomposition of sewage sludge in drying beds at Ley Creek (LC) and Meadowbrook‐Limestone (MB) Wastewater Treatment facilities in metropolitan Syracuse, N.Y. was monitored. LC and MB beds were derived from an anaerobically digested, primary sludge and an aerobically digested, activated sludge, respectively. Fluxes of O2, CH4, and CO2, as determined by in situ incubation of cylinders and analysis by gas chromatography, showed that at LC, aerobic and anaerobic, decomposition and photosynthesis occurred concomitantly due to high moisture. Similar analyses for two separate trials at MB found that both total decomposition rate and percentage of anaerobic decomposition (1 to 90%), as indexed by CH4 evolution vs. O2 consumption, decreased with time and were inversely related to sludge moisture content. O2 consumption rates, when standardized to 15°C, ranged from 10 to 80 µliter/g dry wt. For both LC and MB sludge, aerobic and anaerobic bacteria were abundant (3 × 107 to 6 × 108 colony‐forming units/g dry wt) and dominant bacteria were not enteric. Nematode densities ranged from 7 to 814 individuals/g dry wt.
A computer simulation model on the role of macroinvertebrates in decomposition was used for analyzing the effects of the earthworm, Eisenia foetida. This oligochaete was introduced into one‐half of the MB cylinders and was shown to accelerate decomposition and decrease the proportion of anaerobic decomposition if the sludge was below 375% moisture dry weight and 40% anaerobic decomposition. This stimulation was also reflected in increased nematode density and elevated Eh. Flooding of drying beds caused mortality to E. foetida.
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