P.A. García

New process for simultaneous removal of nitrogen and sulphur under anaerobic conditions

A granular activated carbon (GAC) anaerobic fluidised-bed reactor treating vinasse from an ethanol distillery of sugar beet molasses was operated for 90 days, the first 40 days of start-up followed by 50 days of operation at constant organic loading rate of 1.7g COD/Ld. The reactor showed good performance in terms of organic matter removal but an anomalous behaviour in terms of unusual high concentrations of molecular nitrogen in the biogas. The analysis of the different nitrogenous and sulphur compounds and the mass balances of these compounds in the liquid and gas phases clearly indicated an uncommon evolution of nitrogen and sulphur in the reactor. About 50% of the nitrogen entering the reactor as total Kjeldahl nitrogen (TKN) was removed from the liquid phase appearing as N2 in the gas phase. Simultaneously, only 20% of the S-SO4(2-) initially present in the influent appears as S-S2- in the effluent or S-H2S in the biogas, indicating that 80% of the sulphur is removed. This behaviour has not been reported previously in the literature. These observations may suggest a new anaerobic removal process of ammonia and sulphate according to an uncommon mechanism involving simultaneous anaerobic ammonium oxidation and sulphate reduction.

Assessing carbon and nitrogen removal in a novel anoxic–aerobic cyanobacterial–bacterial photobioreactor configuration with enhanced biomass sedimentation

The carbon and nitrogen removal potential of an innovative anoxic-aerobic photobioreactor configuration operated with both internal and external recyclings was evaluated under different cyanobacterial-bacterial sludge residence times (9-31 days) during the treatment of wastewaters with low C/N ratios. Under optimal operating conditions, the two-stage photobioreactor was capable of providing organic carbon and nitrogen removals over 95% and 90%, respectively. The continuous biomass recycling from the settler resulted in the enrichment and predominance of rapidly-settling cyanobacterial-bacterial flocs and effluent suspended solid concentrations lower than 35 mg VSS L(-1). These flocs exhibited sedimentation rates of 0.28-0.42 m h(-1) but sludge volumetric indexes of 333-430 ml/g. The decoupling between the hydraulic retention time and sludge retention time mediated by the external recycling also avoided the washout of nitrifying bacteria and supported process operation at biomass concentrations of 1000-1500 mg VSS L(-1). The addition of additional NaHCO3 to the process overcame the CO2 limitation resulting from the intense competition for inorganic carbon between cyanobacteria and nitrifying bacteria in the photobioreactor, which supported the successful implementation of a nitrification-denitrification process. Unexpectedly, this nitrification-denitrification process occurred both simultaneously in the photobioreactor alone (as a result of the negligible dissolved oxygen concentrations) and sequentially in the two-stage anoxic-aerobic configuration with internal NO3(-)/NO2(-) recycling.

Anaerobic treatment of cheese whey in a two‐phase uasb reactor

Abstract The whey produced by the cheese industries can be anaerobically treated. The main operational limitations for single phase reactors are instability and the necessity of adding alkalinity. A double phase reactor has been used and a new operational strategy is proposed. The recirculation of the eflluent of the metanization reactor produces a dilution of the influent that allows a good stability of the system without the necessity of adding alkalinity. COD removal higher than 99% can be obtained operating with Bv = 30 Kg m‐3 d‐1 in the acidification reactor (t=0.45 d) and Bv= 15 Kg m‐3 d‐1 in the metanization reactor (t =0.75 d).

Comparison of anaerobic treatment of leachates from an urban-solid-waste landfill at ambient temperature and at 35°C

Abstract The Landfill of Meruelo (Cantabria, Spain) is situated in a warm area. The leachates are produced at a temperature higher than 17°C, even during the winter period. The treatment of the leachates was carried out in a laboratory-scale upflow anaerobic sludge-bed reactor (UASB) at a temperature of 35°C and at ambient temperatures (15–20°C), with the aim of determining the effect of temperature on the COD removal efficiency. At a temperature of 35°C, the organic loading rate was up to 30 kg COD m −3 day −1 and at ambient temperatures organic loading rates were lower than 15 kg COD m −3 day −1 . The average performance of COD removal efficiency was always higher than 82% in both cases, at hydraulic retention times shorter than a day. No nutrients were added to the leachates throughout the study.

Adsorption and Diffusion Effects on the Residence Time Distribution of Submerged Biofilters

The influence of adsorption and diffusion phenomena on the hydrodynamics of a submerged aerated filter was studied by using stimulus-response techniques. Two tracers, lithium chloride and blue-dextran, and two packing materials, sepiolite and puzzolane, were used. The RTD obtained were analyzed by using two theoretical models: the CSTRs (Completely Stirred Tank Reactor) in series model and the CSTRs with dead zone in series model. Experimental results confirmed that the influence of tracer adsorption on the liquid phase hydrodynamics is much smaller than the influence of its diffusion into the packing material. The use of different tracers brought about different results, which were interpreted according to their different diffusional behaviour. In all the experiments, the flow pattern approached to plug-flow. The results obtained from the RTD analysis with both models differed in less than 25% for the experiments done with lithium and sepiolite.