Iñaki Tejero

Anaerobic digestion of the liquid fraction of dairy manure in pilot plant for biogas production: Residual methane yield of digestate

The performance of the only dairy manure biogas plant in Cantabria (Northern coast of Spain) was evaluated in terms of liquid-solid separation and anaerobic digestion of the liquid fraction. Screened liquid fraction was satisfactorily treated in a CSTR digester at HRTs from 20 to 10 days with organic loading rates ranging from 2.0 to 4.5 kg VS/(m(3)d). Stable biogas productions from 0.66 to 1.47 m(3)/(m(3)d) were achieved. Four anaerobic effluents collected from the digester at different HRTs were analyzed to measure their residual methane potentials, which ranged from 12.7 to 102.4 L/gVS. These methane potentials were highly influenced by the feed quality and HRT of the previous CSTR anaerobic digestion process. Biomethanization of the screened liquid fraction of dairy manure from intensive farming has the potential to provide up to 2% of total electrical power in the region of Cantabria.

PARTICLE SIZE DISTRIBUTION OF ACCUMULATED SEDIMENTS ON AN URBAN ROAD IN RAINY WEATHER

Abstract The study of the behavior of deposited sediments on an urban surface serves to determine its characteristics of build‐up, in dry periods, and of wash‐off, during a rain event. Thus, these can be used later to indicate the presence of pollutants in an area. This paper presents data regarding the sediment collected on a road surface in the city of Torrelavega in northern Spain during a period of 65 days during which 132 samples were collected. The rainfall during the sampling period corresponded to 29% of the total rainfall registered in the same year. Two types of sediment collection samples were obtained: vacuumed dry samples (free load) and those swept up following vacuuming (fixed load). For each type of collected sample, the sediment loading, particle size distribution in seven fractions and moisture were determined. The data showed that the sediment loading (g m−2) and vacuumed availability of the load that was more strongly adhered to the surface, “fixed load”, increases with the number of dry days. The particle size distribution of the collected sediment tended to be finer with the increase in number of dry days. Particle sizes less than 125 µm presented the greater rate of accumulation in dry weather and those less than 500 µm, the greater susceptibility to being washed off during a storm event.

Distribution of the concentration of heavy metals associated with the sediment particles accumulated on road surfaces

The heavy metal pollution caused by road run‐off water constitutes a problem in urban areas. The metallic load associated with road sediment must be determined in order to study its impact in drainage systems and receiving waters, and to perfect the design of prevention systems. This paper presents data regarding the sediment collected on road surfaces in the city of Torrelavega (northern Spain) during a period of 65 days (132 samples). Two sample types were collected: vacuum‐dried samples and those swept up following vacuuming. The sediment loading (g m−2), particle size distribution (63–2800 µm) and heavy metal concentrations were determined. The data showed that the concentration of heavy metals tends to increase with the reduction in the particle diameter (exponential tendency). The concentrations of Pb, Zn, Cu, Cr, Ni, Cd, Fe, Mn and Co in the size fraction <63 µm were 350, 630, 124, 57, 56, 38, 3231, 374 and 51 mg kg−1, respectively (average traffic density: 3800 vehicles day−1). By increasing the residence time of the sediment, the concentration increases, whereas the ratio of the concentration between the different size fractions decreases. The concentration across the road diminishes when the distance between the roadway and the sampling siteincreases; when the distance increases, the ratio between size fractions for heavy metal concentrations increases. Finally, the main sources of heavy metals are the particles detached by braking (brake pads) and tyre wear (rubber), and are associated with particle sizes <125 µm.

Comparison between a fixed bed hybrid membrane bioreactor and a conventional membrane bioreactor for municipal wastewater treatment: a pilot-scale study.

A hybrid membrane bioreactor (HMBR) was developed, by adding biofilm support media into a conventional membrane bioreactor (CMBR), and operated in parallel with a CMBR. Results showed that effluent quality was significantly better with the HMBR. The removal efficiencies of COD, BOD5, NH4(+)-N and TN with the HMBR were 84%, 98%, 97% and 75%, respectively, as compared to 80%, 96%, 93% and 38% with the CMBR. There were no differences in phosphorus removal. The membrane fouling rate in the HMBR was on average only 57% of that in the CMBR. The lower concentration of colloidal biopolymer clusters in the HMBR sludge, probably due to their retention by the biofilm, could be partially responsible for this difference. Filterability and settleability of the sludge were also better in the HMBR. Consequently, it is concluded that the addition of fixed support media for biofilm growth can improve the performance of CMBRs.

Effect of mixing on biogas production during mesophilic anaerobic digestion of screened dairy manure in a pilot plant.

The effect of mixing on biogas production of a 1.5‐m3 pilot continuous stirred tank reactor (CSTR) processing screened dairy manure was evaluated. Mixing was carried out by recirculation of reactor content with a mono pump. The experiment was conducted at a controlled temperature of 37±1°C and hydraulic retention times (HRTs) of 20 and 10 days. The effect of continuous and intermittent operation of the recirculation pump on biogas production was studied. At 10 days of HRT, the results showed a minimal influence of recirculation rate on biogas production and that continuous recirculation did not improve reactor performance. At 20 days of HRT, the recirculation rate did not affect reactor performance. Combination of low solid content in feed animal slurry and long HRTs results in minimal mixing requirements for anaerobic digestion.

Hybrid membrane bioreactor application for decentralized treatment and reuse

ABSTRACT Membrane bioreactor (MBR) technology is worldwide recognized, and it is also being applied for reuse purposes. The addition of biofilm support media has already been suggested as pure biofilm as well as hybrid membrane bioreactors (HMBR) in order to get more efficient, compact and stable systems. An original HMBR vertical configuration is here proposed for its feasibility as decentralized treatment, implementing submerged fixed bed biofilm support media (self-produced plastic nets filling the top part of the reactor) and submerged microfiltration membranes (collocated below the support media). The demonstrative treatment plant, tested at increasing loading rates (0.36–1.71 kg COD m −3 d−1), was able to treat municipal wastewater without need of primary settling thus awarding high compactness as required to decentralized treatments. The system maintained good overall performances at increasing loading rates with special regard to organic matter and ammonium removal. Denitrification and total nitro...

The physical factors affecting heavy metals accumulated in the sediment deposited on road surfaces in dry weather: a review

Abstract The main objective of this review is to identify and analyse physical factors (PF) involved in the heavy metal accumulation phenomenon in the road-deposited sediment (RDS) in dry weather. Electronic databases were used to establish an order of prevalence by establishing quartiles (Q-citation frequency) for the PF identified. The results show that the eleven PF can most likely be classified into three categories: climatic-anthropogenic-morphometric. The studies most frequently referenced land use (Q1), rainfall (Q2), particle size (Q2) and vehicles (Q3) as key PF. There is a similar behaviour between the concentrations of Zn-Pb-Cu associated with the RDS in dry weather and the dissolved fraction washed from the surface in road runoff. The size fraction <250 μm is representative of RDS to characterize the metals. The review expands knowledge about the influences of the PF in the processes of deposition-suspension-interception-removal of the metals load in road environments.

Performance evaluation of a novel anaerobic–anoxic sludge blanket reactor for biological nutrient removal treating municipal wastewater

A novel anaerobic-anoxic sludge blanket reactor, AnoxAn, unifies the non-aerated zones of the biological nutrient removal treatment train in a single upflow reactor, aimed at achieving high compactness and efficiency. The environmental conditions are vertically divided up inside the reactor with the anaerobic zone at the bottom and the anoxic zone above. This contribution presents the performance evaluation of the novel reactor in the removal of organic matter and nutrients from municipal wastewater, coupled with an aerobic hybrid MBR. The overall system achieved total nitrogen and phosphorus removal with average efficiencies of 75% and 89%, respectively. Separate anoxic and anaerobic conditions were maintained in AnoxAn, allowing anaerobic phosphate release and nearly complete anoxic denitrification in the single reactor operating with an HRT of 4.2h. Biomass was retained in the reactor achieving TSS concentration up to 10gL(-1) and partial hydrolysis of influent particulate organic matter.

Evaluation of a hybrid vertical membrane bioreactor (HVMBR) for wastewater treatment

A new hybrid membrane bioreactor (HMBR) has been developed to obtain a compact module, with a small footprint and low requirement for aeration. The aim of this research was to assess its performance. The system consists of a single vertical reactor with a filtration membrane unit and, above this, a sponge fixed bed as support medium. The aeration system is located under the membrane unit, allowing for membrane cleaning, oxygenation, biofilm thickness control and bulk liquid mixing. Operated under continuous aeration, a bench-scale reactor (70 L) was fed with pre-treated, raw (unsettled) municipal wastewater. BOD(5) and suspended solids removal efficiencies (96 and 99% respectively) were comparable to those obtained with other membrane bioreactors (MBRs). Total nitrogen removal efficiencies of 80% were achieved, which is better than those obtained in other HMBRs and similar to the values reached using more complex MBRs with extra anoxic tanks, intermittent aeration or internal deflectors.

Cost-effectiveness analysis of sewer mining versus centralized wastewater treatment: Case study of the Arga river basin, Spain

In the context of the EU Water Framework Directive, a cost-effectiveness analysis (CEA) was performed to compare centralized and decentralized wastewater treatment strategies aimed to improve the ecological status of a Spanish river. The implementation of several hybrid membrane bioreactors within the urban framework for sewer mining (SM) was compared with the more common wastewater treatment plant enlargement option. The assessment ranked six alternatives based on 12 potential scenarios, aimed at narrowing the uncertainty of the CEA. The cost analysis illustrated that SM is the most expensive option in regard to both investment and operation and maintenance costs. However, the effectiveness of the alternatives evaluated depends significantly on the scenarios considered, with SM the most effective in most cases. Finally, the cost-effectiveness ratio showed SM as the best cost-effective alternative. CEA provides an ecological-economic indicator useful to prioritize wastewater treatment alternatives to achieve a given objective.