Sebastian Delgado - Academia.edu (original) (raw)

Papers by Sebastian Delgado

Environmental Science and Pollution Research, 2015

Journal of Membrane Science, 2014

An alternative backwashing strategy to enhance water productivity in a tertiary submerged membran... more An alternative backwashing strategy to enhance water productivity in a tertiary submerged membrane bioreactor (MBR) was assayed. This strategy is based on automatically adjustment of the backwashing frequency as a function of the membrane fouling, which is expected to increase the net permeate flux produced. The effect of the key operational parameter (transmembrane pressure set-point, TMP sp) on membrane fouling and process productivity was evaluated on a pilot-scale tertiary MBR. The system was successfully operated for over 4 months with complete sludge retention achieving a high treatment performance with a moderate liquor suspended solid concentration, as a result of carbon substrate limited conditions. The analysis of the membrane fouling at supra-critical filtrate flux of 70 L/(h m 2) with a specific aeration demand identical to that usual at full-scale (SAD pnet ¼ 17 N m 3 /m 3) showed that backwashing efficiency (described in terms of residual fouling resistance) was significantly affected by the selected TMP sp value. At high TMP sp , the efficiency decreased and chemical cleaning was necessary for membrane recovery. Nevertheless, moderate set-point values (30-40 kPa) provided high permeate net fluxes of 65-67 L/(h m 2) for more than 2000 h of operation, while the reversible fouling rate was not considerably influenced by TMP sp. This was also confirmed by flux steps trials. & 2014 Elsevier B.V. All rights reserved. the interrelationships between those parameters and the permeate flux imposed. In fact, due to the complexity of the process, operation strategy is usually time-based and backwashing is commonly applied for 30-60 s every 5.8-15 min of filtration [11]. As a consequence, the systems are not optimised during the whole operational period [1]. Recently, special attention has been paid on feedback control for finding optimal operating conditions in MBRs [12]. Busch and Contents lists available at ScienceDirect

Biomass - Detection, Production and Usage, 2011

Biokinetic models are widely used to design activated sludge process. Knowledge of biokinetics pa... more Biokinetic models are widely used to design activated sludge process. Knowledge of biokinetics parameters allows modelling of the process including the substrate biodegradation rate and biomass growth. At low growth conditions, as is demanded in MBRs, other processes apart from microbial growth have to be taken into consideration. These have been recognized as the maintenance energy requirement, endogenous respiration and subsequent cryptic growth (Van Loosdrecht & Hence, 1999). Macroscopically they cannot be perceived, but, from a practical point of view, the global process can be described by Pirt´s equation (Pirt, 1965). Although there are several experiences with membrane bioreactors working without biomass purge (Rosenberger et al., 2002a; Pollice et al., 2004; Laera et al., 2005), none of these authors apply any kinetics models to describe process performance. Furthermore, these results were obtained in similar conditions, by treating raw municipal wastewater with a high substrate concentration, and it is interesting to compare this behaviour with an MBR treating wastewater with a low organic load. Additionally, not enough is known about the morphology and extracellular polymeric substance (EPS) production for total sludge retention and low F/M ratios. The aim of this chapter is to summarize the current status of membrane bioreactor technology for wastewater treatment (Section 2.1). The advantages against the conventional activated sludge process and technological challenges are assessed (Section 2.2). Some design and operation trends, based on full-scale experience, are reviewed (Section 2.3). To discuss both fundamental aspects, biotreatment and filtration, some experimental results are presented. Special attention was given to the microbial growth modelling (Section 4.1.1), biomass characterisation (Sections 4.1.2 to 4.1.5) and membrane fouling mechanisms (Section 4.2). Some of these results have at the same time been compared with biomass from a conventional activated sludge process (CAS) operated in parallel. 2. Membrane bioreactor (MBR) technology 2.1 Current status and process description The current penetration in the wastewater treatment market of the membrane bioreactors gives an idea of the degree of maturity reached by this technology. The most cited market analysis report indicates an annual growth rate of 13.2 % and predicts a global market value of $ 627 million in 2015 (BCC, 2011). Actually MBRs have been implemented in more than 200 countries (Icon, 2008). Particularly striking is the case of China or some European countries with an implementation rate of over 50% and 20%, respectively. This technological maturity in urban wastewater market is also reflected in two main issues: the diversity of technology suppliers and the upward trend in plant size. Since 1990, the number of MBR membrane module products has grown exponentially until reaching over 50 different providers by the end of 2009 (Judd, 2010). However, globally, the market is dominated by three suppliers: Kubota, Mitsubishi Rayon and GE Zenon, which held about 85-90 % of the urban wastewater market (Pearce, 2008). In regard to the largest MBRs, there are 8 plants with a peak design capacity greater than 50 MLD (Table 1), all of them constructed before 2007 (Judd, 2010). MBR technology is based on the combination of conventional activated sludge treatment together with a process filtration through a membrane with a pore size between 10 nm and 0.4 microns (micro/ultrafiltration), which allows sludge separation. The membrane is a barrier that retains all particles, colloids, bacteria and viruses, providing a complete www.intechopen.com Aerobic Membrane Bioreactor for Wastewater Treatment-Performance Under Substrate-Limited Conditions 267 disinfection of treated water. Furthermore, it can operate at higher concentrations of sludge (up to 12 g/l instead of the usual 4 g/l in conventional systems), which significantly reduces the volume of the reactors and sludge production.

Water Environment Research, 2005

Sulfide generation should be avoided during wastewater transportation. The efficiency of nitrate ... more Sulfide generation should be avoided during wastewater transportation. The efficiency of nitrate dosing for the inhibition of sulfide generation was evaluated during reclaimed wastewater transport with two nitrate doses, 2.5 and 5 mg/L nitrate-nitrogen (NO 3-N). A calcium nitrate [Ca(NO 3) 2 ] solution was injected at the beginning of the 61-km-long gravity pipe, which is part of the Reclaimed Wastewater Reuse System of South Tenerife (Spain). During transportation, after dissolved oxygen depletion, a denitrification process took place. With the 5 mg/L NO 3-N dose, nitrate was not completely removed at the end of the pipe, whereas with 2.5 mg/L NO 3-N, a complete denitrification was achieved. Sulfide generation was completely inhibited with the 5 mg/L dose. However, with 2.5 mg/L, sulfide generation was not completely inhibited but delayed and minimized to a great extent. Denitrification was stoichiometrically limited by the availability in biodegradable matter. An empirical equation enables one to predict the nitrate concentration.

Water Environment Research, 2010

A pilot-scale membrane bioreactor was operated for advanced treatment of secondary effluent from ... more A pilot-scale membrane bioreactor was operated for advanced treatment of secondary effluent from a wastewater treatment plant. The performance and biomass characteristics were evaluated under two different hydraulic retention time (HRT) values (7.5 and 15 hours). The system was operated successfully without biomass purge and, after an initial phase, evolved until reaching a constant mixed-liquor volatile suspended solids (MLVSS) concentration, which resulted in the same value of carbon utilization rate (0.067 6 0.004 kg COD kg 21 MLVSS d 21) for both HRTs. Respiration tests (maximum and endogenous oxygen uptake rates) confirmed a low microbial activity, which approached constant values (0.132 6 0.001 and 0.064 6 0.007 g O 2 g 21 MLVSS d 21 , respectively), regardless of the HRT. The sludge morphology and bound and supernatant extracellular polymeric substances also were assessed. Membrane performance was characterized by a stable behavior occurring simultaneously with a high level of biodegradation in the microcolloidal and soluble fraction. Water Environ. Res., 82, 202 (2010).

Separation and Purification Technology, 2013

ABSTRACT The application of physical cleaning methods such as backflushing or relaxation is an es... more ABSTRACT The application of physical cleaning methods such as backflushing or relaxation is an essential part of the operation mode in submerged membrane bioreactors (SMBRs) applied to wastewater treatment. However, the strategy usually applied for pre-set fixed value of the cleaning frequency involves a loss of water production. This paper deals with the validity of a control system for cleaning initiation by monitoring transmembrane pressure using both physical cleaning methods. To evaluate the effect of the key operational parameter (transmembrane pressure set-point, TMPsp) on membrane fouling and process productivity, sludge samples from a pilot-scale SMBR were filtered under different filtrate flux values (J = 20–40 l h−1 m−2) in bench filtration unit. From this study, it was found that this system automatically adjusts the cleaning frequency as a function of the membrane fouling which results in an increase in the net permeate produced. Cleaning efficiency, described in terms of residual fouling resistance, and the cake fouling rate can be significantly affected by the value of TMPsp selected and the cleaning method performed. A maximal net permeate flux can be achieved when backflushing is used, a filtrate flux above the threshold value of 30 l h−1 m−2 is imposed and intermediate TMPsp values are applied.

Journal of Water Supply: Research and Technology-Aqua, 2012

The integrated management of water resources has taken on great importance in recent years, espec... more The integrated management of water resources has taken on great importance in recent years, especially in insular environments such as the Canary Islands and Madeira, which share geological, environmental, and economic characteristics. Nowadays, due to over-exploitation of aquifers, most of these islands cannot meet their water demand with the traditional resources, forcing their water authorities to establish conservation measures, including water reuse. Several water reuse schemes operate in islands with severe water scarcity, their main applications being in landscape and crop irrigation. However, islands with abundant groundwater resources consider reuse and the advanced treatment it entails as an environmental protection measure, rather than as part of a water saving strategy. This article analyzes the role of water reuse in the management of water resources in the Canary Islands and the Region of Madeira.

Water Science & Technology: Water Supply, 2005

Wastewater reuse provides a substantial non-conventional water resource, mainly for agriculture. ... more Wastewater reuse provides a substantial non-conventional water resource, mainly for agriculture. However, it requires appropriate treatment technologies and previous evaluation so as to meet quality requirements imposed by government regulations and crop needs. Among all the technologies applied to wastewater treatment, membrane-based systems have gained increasing importance, although their main drawback is progressive membrane fouling, which affects process efficiency enormously. The present study analyses the filterability of some biological suspensions as well as the influence of several variables in membrane fouling. Classic dead-end filtration models are used in an attempt to better understand fouling mechanisms and develop methods to prevent or retard it.