Evaluation of anaerobic digestion post-treatment options using an integrated model-based approach

The objective of this paper is to present the main results of an engineering-research project dealing with model-based evaluation of waste streams treatment from a biotech company. This has been extensively done in domestic treatment systems, but is equally important, and with different challenges in industrial wastewater treatment. A new set of biological (activated sludge, anaerobic digestion), physicochemical (aqueous phase, precipitation, mass transfer) process models and model interfaces are required to describe removal of organics in an upflow anaerobic sludge blanket (UASB) reactor plus either traditional nitrification/denitrification (A₁) or partial nitritation (PN)/anammox (ANX) (A₂) processes. Model-based analysis shows that option A₁ requires a decrease in digestion energy recovery (E_recovery) in order to have enough organic substrate for subsequent post NO₃ reduction treatment (95 kWh.kg N^-1). In contrast, A₂ in an aerobic granular sludge reactor allows for higher UASB conversion since N removal is carried out autotrophically. The study also reveals that the addition of an aerated pre-treatment unit prior to the PN/ANX (A₂) reactor promotes COD and H₂S oxidation, CO₂ and CH₄ stripping, a pH increase (up to 8.5) and a reduction of the risk of intra-granular precipitation as well as sulfide inhibition. Simulations indicate clear differences regarding the microbial distribution/abundance within the biofilm in A₂ when comparing the two operational modes. Final results show the effects of different loading and operational conditions; dissolved oxygen (DO), Total Suspended Solids (TSS_op), energy recovery (E_recovery); on the overall process performance; N removal, aeration energy (E_aeration), net energy production (E_recovery); using response surfaces, highlighting the need of integrated approaches to avoid sub-optimal outcomes. The study shows the benefits of virtual plant simulation and demonstrates the potential of model-based evaluation when process engineers in industry have to decide between competing options.

Assessing the effects of intra-granule precipitation in a full-scale industrial anaerobic digester

In this paper, a multi-scale model is used to assess the multiple mineral precipitation potential in a full-scale anaerobic granular sludge system. Reactor behaviour is analysed under different operational conditions (addition/no addition of reject water from dewatering of lime-stabilized biomass) and periods of time (short/long term). Model predictions suggest that a higher contribution of reject water promotes the risk of intra-granule CaCO₃ formation as a result of the increased quantity of calcium arriving with that stream combined with strong pH gradients within the biofilm. The distribution of these precipitates depends on: (i) reactor height; and (ii) granule size. The study also exposes the potential undesirable effects of the long-term addition of reject water (a decrease in energy recovery of 20% over a 100-day period), caused by loss in biomass activity (due to microbial displacement), and the reduced buffer capacity. This demonstrates how both short-term and long-term operational conditions may affect the formation of precipitates within anaerobic granules, and how it may influence methane production and consequently energy recovery.

Modelling an industrial anaerobic granular reactor using a multi-scale approach

The objective of this paper is to show the results of an industrial project dealing with modelling of anaerobic digesters. A multi-scale mathematical approach is developed to describe reactor hydrodynamics, granule growth/distribution and microbial competition/inhibition for substrate/space within the biofilm. The main biochemical and physico-chemical processes in the model are based on the Anaerobic Digestion Model No 1 (ADM1) extended with the fate of phosphorus (P), sulfur (S) and ethanol (Et-OH). Wastewater dynamic conditions are reproduced and data frequency increased using the Benchmark Simulation Model No 2 (BSM2) influent generator. All models are tested using two plant data sets corresponding to different operational periods (#D1, #D2). Simulation results reveal that the proposed approach can satisfactorily describe the transformation of organics, nutrients and minerals, the production of methane, carbon dioxide and sulfide and the potential formation of precipitates within the bulk (average deviation between computer simulations and measurements for both #D1, #D2 is around 10%). Model predictions suggest a stratified structure within the granule which is the result of: 1) applied loading rates, 2) mass transfer limitations and 3) specific (bacterial) affinity for substrate. Hence, inerts (X_I) and methanogens (X_ac) are situated in the inner zone, and this fraction lowers as the radius increases favouring the presence of acidogens (X_su,X_aa, X_fa) and acetogens (X_c4,X_pro). Additional simulations show the effects on the overall process performance when operational (pH) and loading (S:COD) conditions are modified. Lastly, the effect of intra-granular precipitation on the overall organic/inorganic distribution is assessed at: 1) different times; and, 2) reactor heights. Finally, the possibilities and opportunities offered by the proposed approach for conducting engineering optimization projects are discussed.

The Association Between Self-Assessed Future Work Ability and Long-Term Sickness Absence, Disability Pension and Unemployment in a General Working Population: A 7-Year Follow-Up Study

Purpose Work ability is commonly measured with self-assessments, in the form of indices or single items. The validity of these assessments lies in their predictive ability. Prospective studies have reported associations between work ability and sickness absence and disability pension, but few examined why these associations exist. Several correlates of work ability have been reported, but their mechanistic role is largely unknown. This study aims to investigate to what extent individual's own prognosis of work ability predicts labor market participation and whether this was due to individual characteristics and/or working conditions. Methods Self-assessed prognosis of work ability, 2 years from "now," in the Stockholm Public Health Questionnaire (2002-2003) was linked to national registers on sickness absence, disability pension and unemployment up to year 2010. Effects were studied with Cox regression models. Results Of a total of 12,064 individuals 1466 reported poor work ability. There were 299 cases of disability pension, 1466 long-term sickness absence cases and 765 long-term unemployed during follow-up. Poor work ability increased the risk of long-term sickness absence (HR 2.25, CI 95 % 1.97-2.56), disability pension (HR 5.19, CI 95 % 4.07-6.62), and long-term unemployment (HR 2.18, CI 95 % 1.83-2.60). These associations were partially explained by baseline health conditions, physical and (less strongly) psychosocial aspects of working conditions. Conclusions Self-assessed poor ability predicted future long-term sickness absence, disability pension and long-term unemployment. Self-assessed poor work ability seems to be an indicator of future labor market exclusion of different kinds, and can be used in public health monitoring.

Gender differences in lifting technique

The importance of different motion patterns in the assessment of work technique is rarely addressed in the literature and even less information can be found regarding gender differences. In this study the possible gender differences in lifting technique from lifting experiments on 12 female and 10 male participants were examined. The participants performed squat and stoop lifts of a box. Movements were measured by means of opto-electronic measurement systems. Kinematic data derived from the measurements revealed some differences between the men and the women, e.g. in trunk motion and knee angle ranges. The hip-knee interjoint coordination was more synchronized for women than for men in terms of the relative phase angle. It is concluded that so far gender differences in motion patterns have not been sufficiently explored and that men and women need to be considered separately in the evaluation of work technique in manual handling tasks. Advantages and disadvantages of different coordination patterns need to be further investigated.

An observation instrument for assessment of work technique in patient transfer tasks

The aim of the study was to construct an observation instrument for description and assessment of nursing personnel's work technique in patient transfer tasks with regard to musculoskeletal health and safety, and to evaluate the validity and reliability of the instrument. The instrument consists of 24 items arranged in three phases of a transfer: the preparation phase, the starting position and the actual performance. Observations are made from video recordings. A detailed description of the individual's work technique, including actions taken to prepare the transfer, the interaction with the patient and any assistant co-worker, and the motor performance of the nurse, is provided. An attempt was made to quantify the assessments, by calculating an overall score of the work technique with regard to the level of musculoskeletal hazard and safety. The validity and reliability of the instrument were evaluated on 35 video-recorded patient transfers from hospital wards. The validity and reliability were mostly satisfactory, both when evaluating the agreements between the observations of each item (i.e. kappa values > 0.40), and when evaluating the agreements between the overall scores (i.e. intraclass correlation coefficients 0.71-0.90). Further improvements to enhance the agreements are suggested.

Effect of eyelid botulinum toxin injection on lacrimal drainage

PURPOSE

To determine the effect of eyelid botulinum toxin injection on the lacrimal drainage and to assess the use of botulinum toxin in dry eye conditions.

METHODS

Prospectively, three test groups were examined and one lacrimal system investigated in each person in each group. Botulinum toxin A (3.75 IU) was injected into the medial part of 13 lower eyelids of 13 normal test subjects and the medial part of nine lower eyelids in nine patients with dry eyes. A dose of 2.5 IU was injected into the medial part of 10 lower eyelids and the medial part of 10 upper eyelids of 10 patients with dry eyes. The drop test was used to determine the lacrimal drainage capacity and the blink output, before and after the injection. The subjective effect of the botulinum toxin injection on eye comfort was investigated.

RESULTS

Three weeks after lower eyelid botulinum toxin injection, the mean blink output was reduced to 64% (1.19 of 1.87; P <.001) and 70% (0.94 of 1.35; P <.001) of the baseline values in the groups of normal subjects and patients, respectively. After injection in both the upper and lower eyelid, the mean blink output was reduced to 38% (0.54 of 1.41; P <.001) of the baseline value. The patients with dry eyes reported an improved eye comfort in six of nine cases after injection in the lower eyelid and in seven of 10 cases after injection in both the upper and lower eyelid. Adverse effects included one case of increased discomfort for 3 weeks after injection.

CONCLUSION

Injection of botulinum toxin into the medial part of the eyelids decreased the lacrimal drainage, suggesting a new way to treat dry eye conditions. Further studies are required to assess the clinical value of this treatment.

Method and performance: two elements of work technique

In the present study work technique was viewed in two basic elements: the method of carrying out a work task and the individual performance of the work task. The aim was to investigate how eight selected kinematic, kinetic, electromyographic and psychophysical variables can characterize the two elements of work technique. Twelve female subjects lifted a box using two methods, back and leg lifts, and two different simulated performances, fast and slow lifts. Motions, ground reaction forces, muscle activity in the lower back and perceived exertion were measured. A dynamic biomechanical model was applied. The trunk angular displacement and velocity clearly separated the lift methods. The trunk angular velocities and accelerations, the L5/S1 moments and the EMG variables were closely related to the performances. The work technique varied between the subjects to a greater extent than the individual variability over repetitions of a lift task. A larger inter-individual variability for kinematic variables was mostly shown in leg lifts compared with back lifts. The EMG patterns displayed differences in muscle activation that were not revealed by the kinematic or kinetic patterns. The results imply that separate variables should be used for descriptions of work methods and task performances; for method descriptions ranges of motion seem to be appropriate, for performance descriptions displacement time derivatives and load variables seem to be more useful. Moreover, the inter-individual differences suggest that work technique should be evaluated on an individual level.

Telephone advisory service, visits to district nurses and home visits made by district nurses at a Swedish primary health care district

All contacts with the district nurses were registered during a three-week period, daytime Monday to Friday, in a defined primary health care district (Vänersborg, Sweden): 855 incoming telephone calls, 1,016 visits to the district nurses (visits to child welfare unit excluded), and 380 home visits made by the district nurses. The telephone consultations comprised 38% of the total number of contacts and 14% of the time was devoted to this activity, visits to the district nurses at their reception units 45% of all contacts and 39% of the time, and home visits 17% and 47%, respectively. Symptoms from the upper respiratory tract and from the skin were the most common reasons for telephone consultations, while wounds and leg ulcers were the most common reasons for visits to the reception unit and for home visits. A great deal of the district nurse's work was requested by health centres and hospitals.