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

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

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 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

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

A new methodology combining PCR, cloning, and sequencing of clones discriminated by RFLP for the study of microbial populations: application to an UASB reactor sample

This work describes a methodology combining DNA extraction, polymerase chain reaction amplification with primers targeting 16S ribosomal RNA genes, cloning, and sequencing of clones previously analyzed by restriction fragment length polymorphism (RFLP), which can be applied to study the microbial diversity in a given habitat. The methodology allows the minimization of the sequencing effort, which is particularly relevant when analyzing large numbers of clones. The methodology does not require particularly skilled personnel and can easily be adaptable to the molecular characterization of virtually any particular microbial population, provided that both adequate primers and suitable restriction enzymes for RFLP analysis of the clone library have been chosen. An example of application is presented, in which a sample taken from a continuously operating upflow anaerobic sludge blanket reactor was analyzed. RFLP analysis of the initial 162 clones with HaeIII allowed the identification of only 28 distinct profiles. As expected, identical RFLP profiles corresponded to identical nucleotide sequences.publishe

Impact of UASB reactors operation mode on the removal of estrone and 17α-ethinylestradiol from wastewaters

This work aims to compare the performance of the continuous operation (CO) and intermittent operation (IO) of upflow anaerobic sludge blanket (UASB) reactors for the removal of estrone (E1) and 17α-ethinylestradiol (EE2) from wastewaters. Results suggest that the IO contribute to the improvement of the overall removal of estrogens (above 95% for E1 and EE2) when compared to CO (49% for E1 and 39% for EE2). For both CO and IO, biodegradation was the main removal mechanism for E1, while for EE2, adsorption to sludge was the major removal pathway. Moreover, a higher biodegradation of estrogens was obtained with the IO compared to CO (69.4% vs. 43.3% for E1 and 21.8% vs. 8.0% for EE2). The favourable effect of IO can be justified by effluent recirculation during the feedless period which promotes the adaptation of microbial biomass to estrogens' biodegradation.publishe