Assessment of aeration control strategies for biofilm-based partial nitritation/anammox systems.

The objective of this work was to compare the nitrogen removal in mainstream, biofilm-based partial nitritation anammox (PN/A) systems employing (1) constant setpoint dissolved oxygen (DO) control, (2) intermittent aeration, and (3) ammonia-based aeration control (ABAC). A detailed water resource recovery facility (WRRF) model was used to study the dynamic performance of these aeration control strategies with respect to treatment performance and energy consumption. The results show that constant setpoint DO control cannot meet typical regulatory limits for total ammonia nitrogen (NHx-N). Intermittent aeration shows improvement but requires optimisation of the aeration cycle. ABAC shows the best treatment performance with the advantages of continuous operation and over 20% lower average energy consumption as compared to intermittent aeration.

Wastewater as a resource: a unique approach to achieving energy sustainability.

A wastewater-treatment flowsheet was developed to integrate uniquely designed biological processes with physical-chemical unit processes, allowing conversion of the organic carbon in the wastewater to methane, the removal and recovery of phosphorus and nitrogen from the wastewater, and the production of water suitable for reuse. In the flowsheet, energy is derived from the wastewater by first shunting a large fraction of the organic carbon in the wastewater to a solids slurry which is treated via anaerobic digestion. The anaerobic digestion system consists of focused pulsed (FP) pretreatment coupled to anaerobic membrane bioreactors (MBRs). Computer modelling and simulation results are used to optimize design of the system. Energy generation from the system is maximized and costs are reduced by using modest levels of recycle flow from the anaerobic MBRS to the FP pretreatment step.

Treating municipal wastewater with the goal of resource recovery.

A new municipal wastewater treatment flowsheet was developed with the objectives of energy sustainability, and water and nutrient recovery. Energy is derived by shunting a large fraction of the organic carbon in the wastewater to an anaerobic digestion system. Aerobic and anaerobic membrane bioreactors play a key role in energy recovery. Phosphorus and nitrogen are removed from the wastewater and recovered through physical-chemical processes. Computer modeling and simulation results together with energy balance calculations, imply the new flowsheet will result in a dramatic reduction in energy usage at lower treatment plant capital costs in comparison to conventional methods.

Pulse contour cardiac output derived from non-invasive arterial pressure in cardiovascular disease.

Pulse contour methods determine cardiac output semi-invasively using standard arterial access. This study assessed whether cardiac output can be determined non-invasively by replacing the intra-arterial pressure input with a non-invasive finger arterial pressure input in two methods, Nexfin CO-trek and Modelflow , in 25 awake patients after coronary artery bypass surgery. Pulmonary artery thermodilution cardiac output served as a reference. In the supine position, the mean (SD) differences between thermodilution cardiac output and Nexfin CO-trek were 0.22 (0.77) and 0.44 (0.81) l.min(-1) , for intra-arterial and non-invasive pressures, respectively. For Modelflow, these differences were 0.70 (1.08) and 1.80 (1.59) l.min(-1) , respectively. Similarly, in the sitting position, differences between thermodilution cardiac output and Nexfin CO-trek were 0.16 (0.78) and 0.34 (0.83), for intra-arterial and non-invasive arterial pressure, respectively. For Modelflow, these differences were 0.58 (1.11) and 1.52 (1.54) l.min(-1) , respectively. Thus, Nexfin CO-trek readings were not different from thermodilution cardiac output, for both invasive and non-invasive inputs. However, Modelflow readings differed greatly from thermodilution when using non-invasive arterial pressure input.

Continuous non-invasive finger arterial pressure monitoring reflects intra-arterial pressure changes in children undergoing cardiac surgery.

BACKGROUND: Continuous non-invasive measurement of finger arterial pressure (FAP) is a reliable technology in adults. FAP is measured with an inflatable cuff around the finger and simultaneously converted to a reconstructed brachial artery pressure waveform (reBAP) by the Nexfin™ device. We assessed the adequacy of a prototype device (Nexfin-paediatric), designed for a paediatric population, for detecting rapid arterial pressure changes in children during cardiac surgery. METHODS: Thirteen anaesthetized children with a median age of 11 months (2 months-7 yr) undergoing congenital cardiac surgery were included in the study. reBAP and intra-arterial pressure (IAP) were recorded simultaneously during the surgical procedure. To assess the accuracy of reBAP in tracking arterial pressure changes, the four largest IAP variations within a 5 min time interval were identified from each procedure. These variations were compared offline with reBAP during a 10 s control period before and a 10 s period after an arterial pressure change had occurred. RESULTS: In 10 out of 13 children, a non-invasive arterial pressure recording could be obtained. Therefore, recordings from these 10 children were eligible for further analysis, resulting in 40 data points. The correlation coefficient between reBAP and IAP in tracking mean arterial pressure (MAP) changes was 0.98. reBAP followed changes in IAP with a mean bias for systolic, diastolic arterial pressure, and MAP of 0.0 mm Hg (sd 5.8), 0.1 (sd 2.8), and 0.19 (sd 2.7), respectively. CONCLUSIONS: The prototype device closely follows arterial pressure changes in children. However, in a considerable number of attempts, obtaining a signal was time-consuming or unsuccessful. This technique seems promising but requires further technical development.

Fault detection for control of wastewater treatment plants.

Interest in real-time model-based control is increasing as more and more facilities are being asked to meet stricter effluent requirements while at the same time minimizing costs. It has been identified that biological process models and automated process control technologies are being used at wastewater treatments plants throughout the world and that great potential for optimising biotreatment may exist with the integration of these two technology areas. According to our experience, wastewater treatment plants are indeed looking for ways to successfully integrate their modelling knowledge into their process control structure; however, there are practical aspects of this integration that must be addressed if the benefits of this integration are to be realised. This paper discusses the practical aspects of monitoring, filtering and analysing real sensor data with an aim to produce a reliable real-time data stream that might be used within a model-based control structure. Several real case study examples are briefly discussed in this paper.

Anaerobic digestion: a new model for plant-wide wastewater treatment process modelling.

This paper describes a new anaerobic digestion model for wastewater treatment systems (MantisAD). The model has been developed specifically for plant-wide wastewater treatment modelling. That is, rather than modelling nitrogen as a series of fractions of other carbonaceous state variables, this new model includes six dedicated nitrogen state variables. This structure makes this new anaerobic model easier to incorporate into plant-wide models by simplifying the aerobic/anaerobic model interfaces. The model is complete and initial success with the model has been achieved. A comprehensive description of the model including a Petersen Matrix representation of the model is included as is a case study in which the model is applied to full-scale anaerobic digesters.