S. Di Fabio

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

Abstract 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.

Start-up of the completely autotrophic nitrogen removal process using low activity anammox inoculum to treat low strength UASB effluent

The start-up of the completely autotrophic nitrogen removal process was examined in a sequencing batch reactor (SBR) using low activity anoxic ammonium oxidation (anammox) inoculum. The SBR received effluent from an upflow anaerobic sludge blanket (UASB) that treated low strength wastewater. The volumetric nitrogen loading rate (vNLR) was first 0.24 ± 0.11 kg Nm(-3)d(-1) and then reduced to 0.10 ± 0.02 kg Nm(-3)d(-1). The average specific anammox activity was 2.27 ± 1.31 mg N (gVSS h)(-1), at 30°C representing an increase of 161% compared to the inoculum. The decrease in vNLR did not significantly affect anammox activity, but resulted in a decrease of denitrifying heterotrophic activity to very low levels after the first 30 days owing to the decrease of organic loading rate (OLR). Fluorescence in situ hybridization (FISH) analysis confirmed the stable presence of anammox bacteria in biomass. Numerous filamentous microorganisms were present, several of which were in a state of endogenous respiration.

Biological short-cut nitrogen removal from anaerobic digestate in a demonstration sequencing batch reactor

The paper deals with a demonstration study where the nitrogen biological removal from anaerobic supernatants of sewage sludge and organic fraction of the municipal solid waste (OFMSW) was carried out by short-cut nitrification denitrification. The anaerobic supernatant was fed to the demonstration sequencing batch reactor (SBR) directly from the belt press of the full scale municipal WWTP. The SBR had reaction volume of 2.7 m and was engineered on the basis of control algorithms designed by the authors. It was equipped with in-situ probes for the direct ((N-NH4, N-NOx) and indirect (DO, ORP, pH, conductivity) control of biological nitrogen removal. The SBR, inoculated with activated sludge coming from the Treviso municipal wastewater treatment plant (WWTP), treated up to 1.1 kgN/m d and removed more than 90% of the influent total nitrogen, when the oxygen transfer efficiency was not drastically influenced by the liquors salinity. In spite of the different operating and environmental conditions, the effluent showed stable N-NO2/N-NOx ratio higher than 0.9.

Treatment of petrochemical wastewater by employing membrane bioreactors: a case study of effluents discharged to a sensitive water recipient

AbstractThis work was conducted at the largest petrochemical membrane bioreactor (MBR) plant in the world. The effectiveness of MBR technology to treat petrochemical effluents was studied. The treated effluent is discharged in a very sensitive water body and needs to satisfy strict limits. To optimize MBR operation a pilot-scale MBR was set-up that received the same petrochemical effluents as the full scale. In the pre-denitrification configurations, ammonification was not effective. Variable removal of heavy metals/metalloids was obtained by the MBR with As, B, Ba, Mo, Al, Ni, Se, Sb, V and Zn removal being less than 40%, Pb, Hg, Cu, Ag, Cr, Mn and Co removal of 40–70% and only Fe removal being higher than 70%. Sludge clogging was observed in the membrane module; the accumulation of COD, N, P, As, Zn, Mo, Ni, Cd, Sb, Fe, Se and Co in the clogged sludge was higher than that in the activated sludge. The adoption of MBR coupled with suitable physicochemical pre-treatment was able to safeguard the treated ef...