Determination of long-chain fatty acids in anaerobic digester supernatant and olive mill wastewater exploiting an in-syringe dispersive liquid-liquid microextraction and derivatization-free GC-MS method.

Long-chain fatty acids (LCFA) are commonly found in lipid-rich wastewaters and are a key factor to monitor the anaerobic digesters. A new simple, fast, precise, and suitable method for routine analysis of LCFA is proposed. The system involves in-syringe-magnetic stirring-assisted dispersive liquid-liquid microextraction (DLLME) prior to gas chromatography-mass spectrometry (GC-MS) without a derivatization process. Calibration curves were prepared in an ethanol solution (R2 ≥ 0.996), which was also useful as disperser solvent. Hexane was chosen as the extraction solvent. Several parameters (pH, ionic strength, extraction solvent volume, stirring time) were optimized in multivariate and univariate studies. Limits of detection (LODs) were found in the range 0.01-0.05 mg L-1 and good precision inter-day (RSDs≤7.9%) and intra-day (RSDs≤4.4%) were obtained. The method was applied to quantify LCFA in supernatants of anaerobic digesters and olive mill wastewaters (OMW). Palmitic, stearic, and oleic acids were the most abundant fatty acid in the analyzed samples and the relative recoveries for all of them were between 81 and 113%.

[Effects of Long-term Side Stream Extracton on Phosphorus Removal and Recovery Performance of EBPR System].

A sequencing batch reactor (SBR) with alternating anaerobic/oxic (An/O) operation was employed to investigate nitrogen and phosphorus removal performance and corresponding phosphate recovery effect of an enhanced biological phosphorus removal (EBPR) system when extracting side stream ratios of 0, 1/4, 1/3, 1/2 anaerobic phosphorus supernatant. The operation involved three runs within 310 days. Removal efficiencies of COD and NH4+-N were found to be relatively stable over the entire experimental period and effluent could meet standard A of the national discharge standard of pollutants for municipal wastewater treatment plants. Total nitrogen removal improved due to enhancement of denitrification capability during the anaerobic phase, and the standard-reaching rate increased from 88.2% to 98.6%. Although phosphate releasing capability gradually decreased, phosphorus removal performances of the former two runs were stable and efficient. The removal rate was>90% and the corresponding standard-reaching rate was>75%. Nevertheless, phosphorus removal performance began to fluctuate with a side stream ratio of 1/2 during the third run. The lowest phosphorus removal rate was 54.2%, contributing to a 60% non-standard-reaching rate in this run. This suggests that long-term extraction of 1/2 side stream supernatant is not favorable for maintaining stable effluent of the main process. It was also found that long-term phosphate recovery through side stream extraction allowed reduction of sludge mass and had little impact on sludge settling performance. As a result, it is feasible to extract an appropriate side stream ratio of anaerobic supernatant to recover phosphate, combined with efficient removal of both nitrogen and phosphorus in the main process.

Biological nutrients removal from the supernatant originating from the anaerobic digestion of the organic fraction of municipal solid waste.

This study critically evaluates the biological processes and techniques applied to remove nitrogen and phosphorus from the anaerobic supernatant produced from the treatment of the organic fraction of municipal solid waste (OFMSW) and from its co-digestion with other biodegradable organic waste (BOW) streams. The wide application of anaerobic digestion for the treatment of several organic waste streams results in the production of high quantities of anaerobic effluents. Such effluents are characterized by high nutrient content, because organic and particulate nitrogen and phosphorus are hydrolyzed in the anaerobic digestion process. Consequently, adequate post-treatment is required in order to comply with the existing land application and discharge legislation in the European Union countries. This may include physicochemical and biological processes, with the latter being more advantageous due to their lower cost. Nitrogen removal is accomplished through the conventional nitrification/denitrification, nitritation/denitritation and the complete autotrophic nitrogen removal process; the latter is accomplished by nitritation coupled with the anoxic ammonium oxidation process. As anaerobic digestion effluents are characterized by low COD/TKN ratio, conventional denitrification/nitrification is not an attractive option; short-cut nitrogen removal processes are more promising. Both suspended and attached growth processes have been employed to treat the anaerobic supernatant. Specifically, the sequencing batch reactor, the membrane bioreactor, the conventional activated sludge and the moving bed biofilm reactor processes have been investigated. Physicochemical phosphorus removal via struvite precipitation has been extensively examined. Enhanced biological phosphorus removal from the anaerobic supernatant can take place through the sequencing anaerobic/aerobic process. More recently, denitrifying phosphorus removal via nitrite or nitrate has been explored. The removal of phosphorus from the anaerobic supernatant of OFMSW is an interesting research topic that has not yet been explored. At the moment, standardization in the design of facilities that treat anaerobic supernatant produced from the treatment of OFMSW is still under development. To move toward this direction, it is first necessary to assess the performance of alternative treatment options. It study concentrates existing data regarding the characteristics of the anaerobic supernatant produced from the treatment of OFMSW and from their co-digestion with other BOW. This provides data documenting the effect of the anaerobic digestion operating conditions on the supernatant quality and critically evaluates alternative options for the post-treatment of the liquid fraction produced from the anaerobic digestion process.