Adaptive model based control for wastewater treatment plants

In biological wastewater treatment, nitrogen and phosphorous are removed by activated sludge. The process requires oxygen input via aeration of the activated sludge tank. Aeration is responsible for about 60% of the energy consumption of a treatment plant. Hence optimization of aeration can contribute considerably to the increase of energy-efficiency in wastewater treatment. To this end, we introduce an adaptive model based control strategy for aeration called adaptive WOMBAT. The strategy is an improvement of the original WOMBAT, which has been successfully implemented at wastewater treatment plant Westpoort in Amsterdam. In this paper we propose to improve the physics-based model by introducing automatic parameter adaptation. In an experimental model setup the adaptive model based control algorithm proves to result in better effluent quality with less energy consumption. Moreover, it is able to react to the varying circumstances of a real treatment plant and can, therefore, operate without human supervision

Integrated patient-to-room and nurse-to-patient assignment in hospital wards

Assigning patients to rooms and nurses to patients are critical tasks within hospitals that directly affect patient and staff satisfaction, quality of care, and hospital efficiency. Both patient-to-room assignments and nurse-to-patient assignments are typically agreed upon at the ward level, and they interact in several ways such as jointly determining the walking distances nurses must cover between different patient rooms. This motivates to consider both problems jointly in an integrated fashion. This paper presents the first optimization models and algorithms for the integrated patient-to-room and nurse-to-patient assignment problem. We provide a mixed integer programming formulation of the integrated problem that considers the typical objectives from the single problems as well as additional objectives that can only be properly evaluated when integrating both problems. Moreover, motivated by the inherent complexity that results from integrating these two NP-hard and already computationally challenging problems, we devise an efficient heuristic for the integrated patient-to-room and nurse-to-patient assignment problem. To evaluate the running time and quality of the solution obtained with the heuristic, we conduct extensive computational experiments on both artificial and real-world instances. The artificial instances are generated by a parameterized instance generator for the integrated problem that is made freely available

Assigning treatment rooms at the Emergency Department

Increasing efficiency at the Emergency Department (ED) reduces overcrowding. At the ED in typical Dutch Hospitals treatment rooms are mostly shared by two residents of different specialties: a Surgeon and an Internist. Each resident uses multiple rooms in parallel; while one patient awaits test results in a treatment room, the resident visits other patients. The assignment of rooms among the residents is often unbalanced, which affects the blocking probability and waiting and sojourn time of patients. Invoking a queueing model in a random environment, we analytically investigate expected sojourn times of (semi-urgent) patients for both types of residents for different room assignment policies and working routines of the residents. We determine the Pareto efficient policies and working routines for all performance measures. We conduct a Discrete Event Simulation to validate our model and present numerical results for a large Dutch teaching hospital and other illustrative cases

Blocking probabilities in Erlang loss queues with advance reservation

We study the blocking probability in a continuous time loss queue, in which resources can be claimed a random time in advance. We identify classes of loss queues where the advance reservation results in increased or decreased blocking probabilities. The lower blocking probabilities are achieved because the system tends to favor short jobs. We provide analytical and numerical results to establish the connection between the system’s parameters and either an increase or decrease of blocking probabilities, compared to the system without reservation

Slim samenwerken aan een evenwichtige bedbezetting

Een aantal verpleegafdelingen van het Jeroen Bosch Ziekenhuis (JBZ) in ’s Hertogenbosch heeft in 2012 en in het eerste kwartaal van 2013 te maken gehad met een onevenredige bedbezetting. Zowel een (te) hoge als lage bedbezetting is een risico voor de kwaliteit van zorg en arbeid, zoals verderop in dit artikel toegelicht wordt. In opdracht van de specialisten en de manager bedrijfsvoering van het JBZ, en ondersteund door een wiskundige en organisatiedeskundige, is een aantal mogelijke interventies voor het beddenhuis van het JBZ prospectief cijfermatig geanalyseerd. Dit resulteerde in een adequate interventie voor optimalisering van de bedbezetting voor de betrokken specialismen, waardoor de kwaliteit van zorg en arbeid aantoonbaar verbeterd is. In dit artikel worden de gebruikte methoden en de resultaten van het onderzoek kort toegelicht. Zie voor een uitgebreid verslag van het onderzoek hoofdstuk 3 van het proefschrift van Van de Vrugt (Van de Vrugt, 2016)

Static and dynamic appointment scheduling to improve patient access time

Appointment schedules for outpatient clinics have great influence on efficiency and timely access to health care services. The number of new patients per week fluctuates, and capacity at the clinic varies because physicians have other obligations. However, most outpatient clinics use static appointment schedules, which reserve capacity for each patient type. In this paper, we aim to optimise appointment scheduling with respect to access time, taking fluctuating patient arrivals and unavailabilities of physicians into account. To this end, we formulate a stochastic mixed integer programming problem, and approximate its solution invoking two different approaches: (1) a mixed integer programming approach that results in a static appointment schedule, and (2) Markov decision theory, which results in a dynamic scheduling strategy. We apply the methodologies to a case study of the surgical outpatient clinic of the Jeroen Bosch Hospital. We evaluate the effectiveness and limitations of both approaches by discrete event simulation; it appears that allocating only 2% of the capacity flexibly already increases the performance of the clinic significantly

Bezettingsgraad

Het bieden van goede en efficiënte patiëntenzorg vraagt inzicht in procesvariabelen zoals capaciteit, capaciteitsbenutting, beïnvloedbaarheid en sturingsmogelijkheden. Capaciteitsbenutting meet men door het berekenen van de bezettingsgraad. In dit hoofdstuk presenteren we allereerst begrippen met betrekking tot capaciteit en de benutting ervan en een model om deze begrippen aan elkaar te relateren. Met voorbeelden zetten we de stap naar de praktijk van bedrijfsvoering. Conclusies: de norm voor een bezettingsgraad van een afdeling heeft een forse bandbreedte en is in sterke mate situationeel. Hoe kleiner, c.q. hoe specifieker, een afdeling is des te lager zal de bezettingsgraad zijn met de kans op relatief hoge kosten. In de praktijk zien we dat een bezettingsgraad boven de 80 % goed haalbaar is bij de grote interne verpleegafdelingen, maar niet bij kleine, zeer specifieke verpleegafdelingen. Verpleegafdelingen waar geopereerde patiënten verpleegd worden, hebben over het algemeen een lagere bezettingsgraad vanwege weekpatronen in bedbezetting, die in belangrijke mate veroorzaakt worden door het operatierooster. Een bezettingsgraad van 70% is dan realistischer