Treatment of dairy wastewater in UASB reactors inoculated with flocculent biomass

This work assesses the possibility of using flocculent sludge in UASB reactors applied to the treatment of dairy wastewater and studies the effect of hydraulic retention time (6, 8, 12 and 16 h) on the performance of the reactors. The results show that the performance of flocculent sludge is similar to what has been reported in literature for granular sludge. It was observed that by raising the HRT from 6 to 12 h the performance of the system is improved concerning the maximum applicable load, the COD removal efficiency and methane production, but by raising the HRT from 12 to 16 h the differences are not meaningful. To attain soluble COD removals, VFA removals and protein mineralisation near 80% and fat removals above 60% it is necessary to operate the UASB reactors at an HRT of at least 12 h. In addition to this the reactors must be operated at loads under 2.5 g COD/ℓ•d in order to attain a conversion to methane of the removed COD above 70%. Keywords: UASB, hydraulic retention time, optimum load, flocculent biomass, dairy wastewater Water SA Vol. 31(4) 2005: 603-60

Anaerobic removal of 1-methoxy-2-propanol under ambient temperature in an EGSB reactor

Two laboratory-scale expanded granular sludge bed (EGSB) reactors were operated at 18 and 25 C, respectively, for the treatment of synthetic wastewater composed of ethanol and 1-methoxy-2-propanol (M2P) in a mass ratio of 4:1. Reactors were operated first with continuous wastewater supply and after with discontinuous substrate supply (5 days a week, 16 h a day) to simulate shift working conditions. Under continuous wastewater supply chemical oxygen demand (COD), removal efficiency higher than 95 % was achieved at the end of the trial applying organic loading rates (OLR) of 29 and 43 kg COD m-3 day-1 at 18 and 25 C; thus, corresponding to M2P OLR of 6.4 and 9.3 kg COD m-3 day-1, respectively. During intermittent supply of substrate, good performance was recorded at both temperatures with an OLR of 30 kg COD m-3 day-1 (M2P OLR of 6.6 kg COD m-3 day-1). After 56 h without substrate supply, a decline in methane yield of 15¿30 % was observed due to the deactivation of the biomass. Specific methanogenic activity (SMA) assays were carried out at the end of the experiments. SMA values using 1-methoxy-2-propanol as substrate were 24.3 and 7.8 ml CH4 gVSS-1 day-1 at 25 C and at 18 C, respectively. This is the first attempt to investigate the removal of 1-methoxy-2-propanol by EGSB reactors

Acidogenic Fermentation Towards Valorisation of Organic Waste Streams into Volatile Fatty Acids

Anaerobic acidification of eight organic streams (cheese whey, sugarcane molasses, organic fraction of municipal solid wastes (OFMSW), glycerol, soapy slurry, winery wastewater, olive mill effluent, and landfill leachate) was evaluated in batch experiments to determine their acidogenic potential and examine the composition of the produced volatile fatty acids (VFA). Cheese whey, molasses and OFMSW presented the highest acidogenic potentials (0.3 to 0.4 gVFA per g of chemical oxygen demand fed, CODfed) with the predominance of acetic, n-butyric and propionic acids. A further experimental set was applied to cheese whey, by varying food-to-microorganism ratio (F/M) and initial alkalinity. Maximisation of VFA production (up to 0.63 gVFA g–1CODfed) was obtained for an initial alkalinity of 5 – 7 g L–1 as CaCO3 and F/M ratios of 2 – 4 gCOD g–1VSS. Moreover, it was demonstrated that low F/M ratios combined with high alkalinity supply can shift the VFA profile by increasing the production of propionic and n-valeric acids. The results are useful towards optimal designs for acidogenic processes based on the composition of the VFA produced, since the control of the acidification products is crucial for valorisation in some applications

Anaerobic degradation of dairy wastewater in intermittent UASB reactors: influence of effluent recirculation

This work studied the influence of effluent recirculation upon the kinetics of anaerobic degradation of dairy wastewater in the feedless phase of intermittent upflow anaerobic sludge bed (UASB) reactors. Several laboratory-scale tests were performed with different organic loads in closed circuit UASB reactors inoculated with adapted flocculent sludge. The data obtained were used for determination of specific substrate removal rates and specific methane production rates, and adjusted to kinetic models. A high initial substrate removal was observed in all tests due to adsorption of organic matter onto the anaerobic biomass which was not accompanied by biological substrate degradation as measured by methane production. Initial methane production rate was about 45% of initial soluble and colloidal substrate removal rate. This discrepancy between methane production rate and substrate removal rate was observed mainly on the first day of all experiments and was attenuated on the second day, suggesting that the feedless period of intermittent UASB reactors treating dairy wastewater should be longer than one day. Effluent recirculation expressively raised the rate of removal of soluble and colloidal substrate and methane productivity, as compared with results for similar assays in batch reactors without recirculation. The observed bed expansion was due to the biogas production and the application of effluent recirculation led to a sludge bed contraction after all the substrates were degraded. The settleability of the anaerobic sludge improved by the introduction of effluent recirculation this effect being more pronounced for the higher loads

Nitrogen and phosphorus discharge of animal origin in the Baixo Vouga: a spatial data analysis

The livestock production is a strategic and crucial activity for it fixes populations in rural areas, contributing to its conservation, and most importantly because it ensures food production. By producing meat, milk or eggs, this sector contributes to national food self-sufficiency. However, intensive livestock farming activities carry a strong pollution load on the environment, particularly through the emission of nitrogen (N), phosphorus (P), and greenhouse gases (GHG).The Baixo Vouga region in Portugal due to its climatic conditions and soil characteristics holds a high number of livestock production units mainly cattle, poultry and swine. Thus such an activity contributes to a significant portion of the wealth created in this region. This high potential has collided with the existence of environmentally sensitive areas, many of which are protected by European environmental regulations.This work studies the geographical distribution of livestock population of cattle, poultry and swine in the Baixo Vouga region and quantifies its impacts on the environment by calculating the excretion loads of N and P of these species. In the cattle and poultry sectors two clusters or agglomerations are identified, the first in the northern region and the second in the inland region. Moreover, the cattle farming cluster overlaps on vulnerable zones requiring specific monitoring on effluent treatment issues

Effects of organic, hydraulic and fat shocks on the performance of UASB reactors with intermittent operation

Three lab-scale UASB reactors operated at 35°C in an intermittent mode were subject to different step shocks: hydraulic, organic and feed fat content. The results show that the reactors have good resistance to the applied shocks and suggest that a feedless period is beneficial to the performance of the reactors, due to stabilisation of accumulated organic matter.</jats:p