No abstract

No abstract

Small grid-connected photovoltaic systems up to 5 kW p are often not monitored because advanced surveillance systems are not economical. Hence, some system failures which lead to partial energy losses stay unnoticed for a long time. Even a failure that results in a larger energy deficit can be difficult to detect by PV laymen due to the fluctuating energy yields.Within the EU project PVSAT-2, a fully automated performance check has been developed to assure maximum energy yields and to optimize system maintenance for small grid-connected PV systems. The aim is the early detection of system malfunctions and changing operating conditions to prevent energy and subsequent financial losses for the operator. The developed procedure is based on satellitederived solar irradiance information that replaces on-site measurements. In conjunction with a simulation model the expected energy yield of a PV system is calculated. In case of the occurrence of a defined difference between the simulated and actual energy yield, an automated failure detection routine searches for the most probable failure sources and notifies the operator.This paper describes the individual components of the developed procedure-the satellite-derived irradiance, the used PV simulation model, and the principles of the automated failure detection routine. Moreover, it presents results of an 8-months test phase with 100 PV systems in three European countries.

No abstract

Subcritical flux operation is widely practiced in membrane bioreactors (MBRs) to avoid severe membrane fouling and, thus, to maintain sustainable permeability. Filtration at a constant subcritical flux, however, usually leads to a two-stage increase in the transmembrane pressure (TMP): initially slowly, then abruptly. We have investigated the mechanism of this two-stage TMP increase through analyses of the structure and microbial characteristics of the bio-cake formed on the membrane. The MBR was operated under various subcritical and supercritical flux conditions. Under subcritical conditions, we observed the typical two-stage TMP increase. When a constant flux augmented and reached the supercritical conditions, however, the dual TMP change gradually transformed into a steeper, one-stage TMP increase. The second stage TMP increase under the subcritical flux was closely related to the sudden increase in the concentration of extra-cellular polymeric substances (EPSs) at the bottom layer of the bio-cake; we attribute the one-stage TMP increase under the supercritical conditions to the accumulation of microbial flocs and the reduced porosity of the bio-cake under compression. We explain the variation of the EPS concentration in the bio-cake in terms of the spatial and temporal changes of the live-to-dead ratio along the depth of the bio-cake.

No abstract

Ten biomass samples from both municipal and industrial pilot and full scale submerged membrane bioreactors (MBRs) with mixed liquor suspended solids concentrations (MLSS) ranging from 7.2 to 30.2g L(-1) were studied at six air-flow rates (0.7, 1.3, 2.3, 3, 4.4 and 6m(3)m(-3)h(-1)). Statistical analyses were applied to identify the relative impacts of the various bulk biomass characteristics on oxygen transfer. Of the biomass characteristics studied, only solids concentration (correlated with viscosity), the carbohydrate fraction of the EPS (EPS(c)) and the chemical oxygen demand (COD) concentration of the SMP (SMP(COD)) were found to affect the oxygen transfer parameters k(L)a(20) (the oxygen transfer coefficient) and alpha-factor. The relative influence on k(L)a(20) was MLSS>aeration>EPS(c)>SMP(COD) and on alpha-factor was MLSS>SMP(COD)>EPS(c)>aeration. Both k(L)a(20) and alpha-factor increased with increasing aeration and EPS(c) and decreased with increasing MLSS and SMP(COD). MLSS was found to be the main parameter controlling the oxygen transfer.

No abstract