J.H.J.M. van der Graaf

Impact of inflow conditions on activated sludge filterability and membrane bioreactor (MBR) operational performance

Operation and performance of membrane bioreactors (MBRs) for wastewater treatment is influenced by changes in activated sludge properties. Therefore, understanding of the factors influencing sludge filterability is of major importance for efficient operation of MBR installations. This paper assesses the impact of the influent characteristics on activated sludge filterability and treatment performance of full-scale MBRs. The full-scale MBRs were closely monitored both in summer and winter. The measurement campaign, consisting of activated sludge filterability tests and physicochemical analyses, is supplemented with operational performance data evaluation of the various full-scale plants. Based on these data, it is shown that an undesired and refractory composition of incoming wastewater, hydraulic and/or organic load shocks, as well as abrupt temperature changes of the influent, lead to operational problems and affect sludge filterability.

Direct Wastewater Membrane Filtration for Advanced Particle Removal from Raw Wastewater

Direct filtration techniques were applied for fast and advanced particle removal in the pre-treatment of municipal wastewater, in order to optimise the total wastewater treatment system. Pilot-scale research into direct membrane ultrafiltration of raw wastewater indicated that this technique might be feasible. There was an average normalised production flux of 300 l/m2·h·bar at a TMP of 0.2 to 0.4 bar and a cross flow rate of 2.4 m/s. Removal performances were excellent with all suspended and colloidal substances being removed by the membranes with pore size of 30 nm. Furthermore the influence of the cross flow rate, the applied TMP and the cleaning procedure on the filtration performance was investigated. It was concluded that direct membrane filtration shows potential for wastewater treatment.

MBR performance: Operational problems in industry

A major study undertaken by a number of institutions and a leading engineering consultancy has investigated factors affecting the performance in operation of membrane bioreactors in a variety of different industrial applications. Jose Antonio Gil summarises the findings.

Identification and Evaluation of Wastewater Scenarios, Based on Physical-Chemical Pretreatment

The purpose of the present research project was to identify new, more sustainable wastewater treatment scenarios by literature research, contacting international experts, and finally evaluating the scenarios according to certain scenarios.

Phosphorus and nitrogen profile measurements to locate phosphorus limitation in a fixed bed filter

The European Union presented in 2000 the European Water Framework Directive (WFD). Within the WFD approach the focus is more and more on ultra low nitrogen (<2.2 mg N-total/L) and phosphorus concentrations (<0.15 mg P-total/L) in waste water treatment plant (WWTP) effluent. Nitrogen concentrations of 2.2 mg N-total/L can be reached with denitrifying filters as a tertiary treatment step. When combining nitrogen and chemical phosphorus removal in a filter, phosphorus limitation may occur. After nitrite accumulation, caused by phosphorus limitation, was measured in the filtrate water of the dual media filter, research was started to locate, to understand and to solve the problem. Profile measurements for nitrate, nitrite and orthophosphorus (PO(4)-P) combined with COD and O(2) were conducted. Results show that the minimal required PO(4)-P/NO(x)-N ratio is 0.006 mg/mg after coagulation and flocculation. Profile measurements have proven to be a useful tool. It showed how nitrate and orthophosphorus are removed through the filter bed and it showed the consequences for the PO(4)-P/NO(x)-N ratio. When orthophosphorus is removed more rapidly compared to nitrate the PO(4)-P/NO(x)-N ratio decreases. When the PO(4)-P/NO(x)-N ratio becomes below 0.006 mg/mg for a certain period of time, orthophosphorus limitation occurs. The solution can be either changing the filter bed configuration or decreasing the coagulant dosage.

Start-up of decentralised MBRs Part II: the use of additives as initial inoculum

Abstract This paper corresponds to the second part of a study aiming to establish the best conditions to start-up decentralised membrane bioreactors. The first part focused on the impact of different operational parameters on the start-up, whereas this second part aims to find a substitute for activated sludge to serve as initial inoculum. Both low powdered activated carbon addition and Alumin 7 (alkaline coagulant) demonstrated a low performance in terms of filterability and operation. In turn, ferrous chloride (FeCl2), due to its ability to coagulate soluble and colloidal matter, was able to create a cake layer composed of large coagulated particles acting as a prefilter. Additionally, the combination of wastewater plus FeCl2 allowing sufficient contact time before the filtration starts has demonstrated to be the best way to start-up decentralised membrane bioreactor using this additive. Eventhough some drawbacks are associated with its high acidity, i.e. low pH, high conductivity and low removal, the e...