Effects of earthworms on surface clogging characteristics of intermittent sand filters.

Intermittent sand filters (ISFs) are effective and economical in treating wastewater, but they are easy to clog up. To explore a feasible and simple method to alleviate clogging, two pilot-scale ISFs were constructed, one of which contained earthworms and the other did not. During the operation, the effects of earthworms on the hydraulic behaviour of ISFs were investigated. The results showed that both ISFs exhibited good performance in wastewater treatment. However, they showed different hydraulic characteristics although operated at the same organic loading rate (approximately 300 g m(-2) d(-1)). The ISF without earthworms clogged only after 53 d operation, and was partially recovered after 7 d resting, but after that, clogging occurred again, and more rapidly than the initial clogging event (40 d). However, water on the medium surface of the ISF with earthworms was not observed during the whole experiments. In addition, 11-13% of effective porosity and 0.015-0.026 cm s(-1) of infiltration rate were measured in the upper 20 cm of the ISF at the end of the experiments. The facts demonstrated that earthworms played a positive role in alleviating clogging and earthworms fed filter could alleviate surface clogging effectively.

Excess nitrogen accumulation in activated sludge in sequencing batch reactor with a single-stage oxic process.

It was occasionally found that a significant nitrogen loss in solution under neutral pH value in a sequencing batch reactor with a single-stage oxic process using synthetic wastewater, and then further studies were to verify the phenomenon of nitrogen loss and to investigate the pathway of nitrogen removal. The result showed that good performance of nitrogen removal was obtained in system. 0-7.28 mg L(-1) ammonia, 0.08-0.38 mg L(-1) nitrite and 0.94-2.12 mg L(-1) nitrate were determined in effluent, respectively, when 29.85-35.65 mg L(-1) ammonia was feeding as the sole nitrogen source in influent. Furthermore, a substantial nitrogen loss in solution (95% of nitrogen influent) coupled with a little gaseous nitrogen increase in off-gas (7% of nitrogen influent) was determined during a typical aerobic phase. In addition, about 322 mg nitrogen accumulation (84% of nitrogen influent) was detected in activated sludge. Based on nitrogen mass balance calculation, the unaccounted nitrogen fraction and the ratio of nitrogen accumulation in sludge/nitrogen loss in solution were 14.6 mg (3.7% of nitrogen influent) and 0.89, respectively. The facts indicated that the essential pathway of nitrogen loss in solution in this study was excess nitrogen accumulation in activated sludge.

[Biological nitrogen removal with excess nitrogen uptake by microorganisms].

The performance of nitrogen removal with sequencing batch reactors were investigated in different pH conditions using simulated municipal wastewater. The experimental results showed that ammonium and nitrate as well as nitrite in R2 (pH controlled at 8.0 +/- 0.2) were 0-1 mg x L(-1) and 8-10 mg x L(-1) respectively, while ammonium and nitrate as well as nitrite in R1 (pH controlled at 7.0 +/- 0.2) were 0-5 mg x L(-1) and 1-2 mg x L(-1) respectively under the operational process of 4-hour aeration --> 4-hour settle/idle phase, which indicated the removal rates of TIN (TIN = NH4+ -N + NO3- -N + NO2- -N) in R1 and R2 were above 85% and about 70% respectively, when the COD and ammonium concentrations in influent were 250-300 mg x L(-11), 30-40 mg x L(-1), respectively. Total nitrogen in sludge was at a high level and increased in the aeration after decreasing in the first hour aeration, the content of total nitrogen in sludge was 214 mg x g(-1) at the beginning of aerobic phase, 210 mg x g(-1) in the first aeration and 215 mg x g(-1) at the end. The researches indicated that high efficiency of nitrogen removal could be obtained in sequencing batch reactor and nitrogen removal in this study was not realized by traditional nitrification/denitrification approach but by the discharge of rich-nitrogen sludge.

The probable metabolic relation between phosphate uptake and energy storages formations under single-stage oxic condition.

To investigate the possible biochemical metabolisms for excess phosphate uptake in a sequencing batch reactor (SBR) with single-stage oxic process, which was reported using glucose as the sole carbon source previously, glucose and acetate were fed to two SBRs as the sole carbon source, respectively. The changes of polyhydroxyalkanoates (PHAs), glycogen and the removal of phosphorus were compared between two SBRs. It was observed that the phosphorus removal efficiency was 91.8-94.4% with glucose, and 23.3-28.5% with acetate, although the former showed much lower accumulations/transformations of PHAs. Instead, the former showed a much higher transformation of glycogen. The facts suggested that glycogen could replace PHAs to supply energy for phosphate uptake under the single-stage oxic condition. Furthermore, the possible biochemical metabolisms were proposed to describe the relation between phosphate uptake and energy storages formations under such a single-stage oxic process. Such a process may serve as a prototype for the development of alternative biological and chemical options for phosphate removal from wastewaters.

[DNA extraction methods of compost for molecular ecology analysis].

Molecular ecology provides new techniques for studying compost microbes, and the DNA extraction is the basis of molecular techniques. Because of the contamination of humic acids, it turns to be more difficult for compost microbial DNA extraction. Three different approaches, named as lysozyme lysis, ultrasonic lysis and proteinase K lysis with CTAB, were used to extract the total DNA from compost. The detection performed on a nucleic acids and protein analyzer showed that all the three approaches produced high DNA yields. The agarose gel electrophoresis showed that the DNA fragments extracted from compost had a length of about 23 kb. A eubacterial 16S rRNA gene targeted primer pair (27F and 1 495R) was used for PCR amplification, and all the samples got almost the full length 16S rDNA sequence (about 1.5 kb). After digested by restriction endonucleases (Hae Ill and Alu I), the restriction map showed relatively identical microbial diversity in the DNA, which was extracted by the three different approaches. All the compost microbial DNA extracted by the three different approaches could be used for molecular ecological study, and researchers should choose the right approach for extracting microbial DNA from compost based on the facts.