Adults living with Duchenne muscular dystrophy: old and new challenges in a cohort of 19 patients in their third to fifth decade

BACKGROUND AND PURPOSE

Advances in multidisciplinary care are extending overall survival in Duchenne muscular dystrophy (DMD) patients. Our research objective was to delineate the clinical characteristics of this particular cohort and identify novel challenges associated with the disease.

METHODS

Nineteen individuals aged 25-48 years (median 34 years) with a confirmed diagnosis of out-of-frame DMD gene mutation were selected.

RESULTS

All patients were mechanically ventilated (5/19 via tracheostomy), with different patterns of cardiomyopathy. Swallowing and nutritional issues were frequent (median body mass index 18.95), with six cases requiring artificial enteral feeding (median age at start 29 years), as well as bone density alterations (11/19, 58%). Only 2/19 had been on long-term prednisone therapy. Issues requiring at-home/hospital assistance were respiratory infections (15/19, 79%), gastroenterological symptoms (9/19, 47%, including toxic megacolon and rectal perforation after repeated enemas), metabolic acidosis (2/19, 11%) and recurrent ischaemic strokes (1/19, 5%). From a social perspective, augmented-alternative communication devices were necessary for 7/19 (37%), with most of the patients being assisted at home and 2/19 institutionalized. Eight/19 (42%) patients experienced psychiatric symptoms (median age at presentation 16 years) and 9/19 (47%) chronic pain (median age at onset 23 years), in both cases treated with psychoactive/analgesic drugs without major adverse events. The patients' subjective perception of physical health resulted in unfavourable scores, whilst the subjective assessment of mental health unexpectedly showed more positive values compared to other chronic neurological conditions.

CONCLUSIONS

The analysis of adults living with DMD reveals several new health-related issues, such as the management of emergencies and safety of pharmacological treatments for psychiatric symptoms, chronic pain management, as well as an increasing caregivers burden.

Gain and loss of upper limb abilities in Duchenne muscular dystrophy patients: A 24-month study

Duchenne muscular dystrophy (DMD) is a neuromuscular condition characterized by muscle weakness. The Performance of upper limb (PUL) test is designed to evaluate upper limb function in DMD patients across three domains. The aim of this study is to identify frequently lost or gained PUL 2.0 abilities at distinct functional stages in DMD patients. This retrospective study analyzed prospectively collected data on 24-month PUL 2.0 changes related to ambulatory function. Ambulant patients were categorized based on initial 6MWT distance, non-ambulant patients by time since ambulation loss. Each PUL 2.0 item was classified as shift up, no change, or shift down. The study's cohort incuded 274 patients, with 626 paired evaluations at the 24-month mark. Among these, 55.1 % had activity loss, while 29.1 % had gains. Ambulant patients showed the lowest loss rates, mainly in the shoulder domain. The highest loss rate was in the shoulder domain in the transitioning subgroup and in elbow and distal domains in the non-ambulant patients. Younger ambulant patients demonstrated multiple gains, whereas in the other functional subgroups there were fewer gains, mostly tied to singular activities. Our findings highlight divergent upper limb domain progression, partly linked to functional status and baseline function.

Longitudinal Analysis of PUL 2.0 Domains in Ambulant and Non-Ambulant Duchenne Muscular Dystrophy Patients: How do they Change in Relation to Functional Ability?

BACKGROUND

The performance of upper limb 2.0 (PUL) is widely used to assess upper limb function in DMD patients. The aim of the study was to assess 24 month PUL changes in a large cohort of DMD patients and to establish whether domains changes occur more frequently in specific functional subgroups.

METHODS

The PUL was performed in 311 patients who had at least one pair of assessments at 24 months, for a total of 808 paired assessments. Ambulant patients were subdivided according to the ability to walk: >350, 250-350, ≤250 meters. Non ambulant patients were subdivided according to the time since they lost ambulation: <1, 1-2, 2-5 or >5 years.

RESULTS

At 12 months, the mean PUL 2.0 change on all the paired assessments was -1.30 (-1.51--1.05) for the total score, -0.5 (-0.66--0.39) for the shoulder domain, -0.6 (-0.74--0.5) for the elbow domain and -0.1 (-0.20--0.06) for the distal domain.At 24 months, the mean PUL 2.0 change on all the paired assessments was -2.9 (-3.29--2.60) for the total score, -1.30 (-1.47--1.09) for the shoulder domain, -1.30 (-1.45--1.11) for the elbow domain and -0.4 (-1.48--1.29) for the distal domain.Changes at 12 and 24 months were statistically significant between subgroups with different functional abilities for the total score and each domain (p <  0.001).

CONCLUSION

There were different patterns of changes among the functional subgroups in the individual domains. The time of transition, including the year before and after loss of ambulation, show the peak of negative changes in PUL total scores that reflect not only loss of shoulder but also of elbow activities. These results suggest that patterns of changes should be considered at the time of designing clinical trials.

Technology-outcome measures in neuromuscular disorders: a systematic review

BACKGROUND

Portable and wearable devices can monitor a number of physical performances and have been lately applied to patients with neuromuscular disorders (NMD).

METHODS

We performed a systematic search of literature databases following PRISMA principles, including all studies reporting the use of technological devices for motor function assessment in NMDs from 2000 to 2021. We also summarized the evidence on measurement properties (validity, reliability, responsiveness) of the analyzed technological outcome measures.

RESULTS

One-hundred studies fulfilled the selection criteria, most of them published in the last ten years. We defined four categories that gathered similar technologies: gait analysis tools, for clinical assessment of pace and posture; continuous monitoring of physical activity with inertial sensors, that allow "unsupervised" activity assessment; upper limb evaluation tools, including Kinect-based outcome measures to assess the reachable workspace; and new muscle strength assessment tools, such as Myotools. Inertial sensors have the evident advantage of being applied in the "in-home" setting, which has become especially appealing with the Covid-19 pandemic, although poor evidence from psychometric property assessment and results of the analyzed studies may limit their research application. Both Kinect-based outcome measures and Myotools have been already validated in multicenter studies and different NMDs, showing excellent characteristics for application in clinical trials.

CONCLUSION

This overview is intended to raise awareness on the potential of the different TOMs in the neuromuscular field and be an informative source for the design of future clinical trials, particularly in the era of telemedicine.

Functional assessment tools in children with Pompe disease: A pilot comparative study to identify suitable outcome measures for the standard of care

BACKGROUND

Pompe disease (PD) is a rare condition caused by mutations in gene encoding for the enzyme alpha-glucosidase, resulting in an abnormal intracellular accumulation of glycogen. The disease clinical spectrum ranges from severe infantile forms to adult-onset forms with minor limitations. Since 2000 enzyme replacement therapy (ERT) is available and disease natural history has changed, with prolonged survival and evidence of myopathic features.

METHODS

In this study, we monitored disease progression up to three years in eight young patients with PD. Based on the literature data and the long term personal experience, we selected validated functional scales for neuromuscular disorders and compared the results to identify a simple and reliable protocol for the follow-up of children with PD. Moreover, we evaluated cognitive functions using developmental/cognitive tests.

RESULTS

Based on study results, we suggest that motor functions in children with PD could be better assessed by Chop Intend, MFM20 (Motor Function Measure Scale for Neuromuscular Diseases 20) and NSAA (North Star Ambulatory Assessment), according to age and functional level. Evaluation should be completed with ROM (Range Of Motion) measurement, MRC (Medical Research Council) evaluation and 6MWT (6 Minute Walk test) when possible.

CONCLUSIONS

The proposed protocol seems to be reliable and should be done every six months, because of the progressive natural history of the disease, the rapid changes typical of developmental age and the need to document ERT effects. About cognitive functions, additional tests to classical intelligence scales (WISC, WPPSI) should be useful to better describe specific neuropsychological profile.

Upper limb function in Duchenne muscular dystrophy: 24 month longitudinal data

The aim of the study was to establish 24 month changes in upper limb function using a revised version of the performance of upper limb test (PUL 2.0) in a large cohort of ambulant and non-ambulant boys with Duchenne muscular dystrophy and to identify possible trajectories of progression. Of the 187 patients studied, 87 were ambulant (age range: 7–15.8 years), and 90 non-ambulant (age range: 9.08–24.78). The total scores changed significantly over time (p<0.001). Non-ambulant patients had lower total scores at baseline (mean 19.7) when compared to the ambulant ones (mean 38.4). They also had also a bigger decrease in total scores over 24 months compared to the ambulant boys (4.36 vs 2.07 points). Multivariate model analysis showed that the Performance of Upper Limb changes reflected the entry level and ambulation status, that were independently associated to the slope of Performance of Upper Limb changes. This information will be of help both in clinical practice and at the time of designing clinical trials.

Benefits of glucocorticoids in non-ambulant boys/men with Duchenne muscular dystrophy: A multicentric longitudinal study using the Performance of Upper Limb test

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The paper reports the effect of steroids on upper limb function in non ambulant DMD boys.

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Boys continuing steroids after loss of ambulation perform better than those who stopped at the time of loss of ambulation.

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The Performance of Upper Limb test can reliably capture change over time and the effect of intervention.

The aim of this study was to establish the possible effect of glucocorticoid treatment on upper limb function in a cohort of 91 non-ambulant DMD boys and adults of age between 11 and 26 years.

All 91 were assessed using the Performance of Upper Limb test. Forty-eight were still on glucocorticoid after loss of ambulation, 25 stopped steroids at the time they lost ambulation and 18 were GC naïve or had steroids while ambulant for less than a year.

At baseline the total scores ranged between 0 and 74 (mean 41.20). The mean total scores were 47.92 in the glucocorticoid group, 36 in those who stopped at loss of ambulation and 30.5 in the naïve group (p < 0.001).

The 12-month changes ranged between −20 and 4 (mean −4.4). The mean changes were −3.79 in the glucocorticoid group, −5.52 in those who stopped at loss of ambulation and −4.44 in the naïve group. This was more obvious in the patients between 12 and 18 years and at shoulder and elbow levels.

Our findings suggest that continuing glucocorticoids throughout teenage years and adulthood after loss of ambulation appears to have a beneficial effect on upper limb function.

Long term natural history data in ambulant boys with Duchenne muscular dystrophy: 36-month changes

The 6 minute walk test has been recently chosen as the primary outcome measure in international multicenter clinical trials in Duchenne muscular dystrophy ambulant patients. The aim of the study was to assess the spectrum of changes at 3 years in the individual measures, their correlation with steroid treatment, age and 6 minute walk test values at baseline. Ninety-six patients from 11 centers were assessed at baseline and 12, 24 and 36 months after baseline using the 6 minute walk test and the North Star Ambulatory Assessment. Three boys (3%) lost the ability to perform the 6 minute walk test within 12 months, another 13 between 12 and 24 months (14%) and 11 between 24 and 36 months (12%). The 6 minute walk test showed an average overall decline of -15.8 (SD 77.3) m at 12 months, of -58.9 (SD 125.7) m at 24 months and -104.22 (SD 146.2) m at 36 months. The changes were significantly different in the two baseline age groups and according to the baseline 6 minute walk test values (below and above 350 m) (p<0.001). The changes were also significantly different according to steroid treatment (p = 0.01). Similar findings were found for the North Star Ambulatory Assessment. These are the first 36 month longitudinal data using the 6 minute walk test and North Star Ambulatory Assessment in Duchenne muscular dystrophy. Our findings will help not only to have a better idea of the progression of the disorder but also provide reference data that can be used to compare with the results of the long term extension studies that are becoming available.

6 Minute walk test in Duchenne MD patients with different mutations: 12 month changes

OBJECTIVE

In the last few years some of the therapeutical approaches for Duchenne muscular dystrophy (DMD) are specifically targeting distinct groups of mutations, such as deletions eligible for skipping of individual exons. The aim of this observational study was to establish whether patients with distinct groups of mutations have different profiles of changes on the 6 minute walk test (6MWT) over a 12 month period.

METHODS

The 6MWT was performed in 191 ambulant DMD boys at baseline and 12 months later. The results were analysed using a test for heterogeneity in order to establish possible differences among different types of mutations (deletions, duplications, point mutations) and among subgroups of deletions eligible to skip individual exons.

RESULTS

At baseline the 6MWD ranged between 180 and 560,80 metres (mean 378,06, SD 74,13). The 12 month changes ranged between -325 and 175 (mean -10.8 meters, SD 69.2). Although boys with duplications had better results than those with the other types of mutations, the difference was not significant. Similarly, boys eligible for skipping of the exon 44 had better baseline results and less drastic changes than those eligible for skipping exon 45 or 53, but the difference was not significant.

CONCLUSIONS

even if there are some differences among subgroups, the mean 12 month changes in each subgroup were all within a narrow Range: from the mean of the whole DMD cohort. This information will be of help at the time of designing clinical trials with small numbers of eligible patients.

SBR treatment of olive mill wastewaters: dilution or pre-treatment?

The olive-oil extraction industry is an economically important activity for many countries of the Mediterranean Sea area, with Spain, Greece and Italy being the major producers. This activity, however, may represent a serious environmental problem due to the discharge of highly polluted effluents, usually referred to as 'olive mill wastewaters' (OMWs). They are characterized by high values of chemical oxygen demand (COD) (80-300 g/L), lipids, total polyphenols (TPP), tannins and other substances difficult to degrade. An adequate treatment before discharging is therefore required to reduce the pollutant load. The aim of the present paper was to evaluate performances of a biological process in a sequencing batch reactor (SBR) fed with pre-treated OMWs. Pre-treatment consisted of a combined acid cracking (AC) and granular activated carbon (GAC) adsorption process. The efficiency of the system was compared with that of an identical SBR fed with the raw wastewater only diluted. Combined AC and GAC adsorption was chosen to be used prior to the following biological process due to its capability of providing high removal efficiencies of COD and TPP and also appreciable improvement of biodegradability. Comparing results obtained with different influents showed that best performances of the SBR were obtained by feeding it with raw diluted OMWs (dOMWs) and at the lowest dilution ratio (1:25): in this case, the removal efficiencies were 90 and 76%, as average, for COD and TPP, respectively. Feeding the SBR with either the pre-treated or the raw dOMWs at 1:50 gave very similar values of COD reduction (74%); however, an improvement of the TPP removal was observed in the former case.

The Biological Aerated Filter (BAF) as alternative treatment for domestic sewage. Optimization of plant performance

The aim of the present study was to investigate the suitability of a Biological Aerated Filter (BAF) plant as an alternative process or an upgrading step for the treatment of domestic wastewater from the city of Rome, Italy. The results obtained through a three years experimental activity on a pilot-scale BAF plant fed with real wastewater showed high process efficiencies and stable performance for both carbon and ammonia oxidation. The effluent quality met, on average basis, 68 mg/L total COD (COD(tot)), 37 mg/L Total Suspended Solids (TSS), 3.3mg/L ammonia-nitrogen (NH(4)(+)-N) and 21.1mg/L nitrate-nitrogen (NO(3)(-)-N). Despite the good performance, the high content of suspended solids in the influent stream caused filter bed clogging and frequent backwashing operations were required. Therefore, in the last part of the experimental activity a pre-treatment step was adopted prior to the biological step, consisting of chemical precipitation by lime addition. The influent quality parameters were consequently modified; for instance the particulate matter content was reduced by about 73%. The process efficiency of both ammonia and organic carbon oxidation did not modify appreciably; however, a beneficial effect was obtained on the frequency of the backwashing phase, which could be reduced by half. Since the new combined chemical-biological system demonstrated to be a valid alternative to the activated sludge treatment plant, a modeling activity was finally performed with the aim of evaluating the design parameters of a full-scale BAF plant fed with the same pre-treated wastewater as used in the experimental activity. The results of this phase are also herewith presented and discussed.

Remediation of chlorophenol- and phenol-contaminated groundwater by a sequencing batch biofilm reactor

The paper describes the results of an investigation aimed at evaluating suitability of a lab-scale Sequencing Batch Biofilm Reactor (SBBR) for the remediation of groundwater contaminated by phenol (P) and 2-chlorophenol (2-CP). Kinetics of compound degradation was determined along the bed height in the absence and in presence of effluent recirculation, and with different influent composition (compounds fed separately or in combination in the same stream). SBBR performances with and without recirculation were very satisfactory for all the influent compositions: the system showed 99% removal efficiencies for both phenol and 2-CP and their complete removal was always achieved far before the end of react. In the presence of recirculation, the concentration gradient established during fill was rapidly eliminated and an even biomass distribution along the bed height was formed. Consequently, an acceleration of the elimination process was observed, particularly for phenol that was mostly removed in the first hour of the cycle. When the compounds were fed simultaneously, 2-CP removal kinetics improved probably due to cometabolism. The adsorption phenomena of the toxic compounds on the packing material were studied also, showing about 50% COD removal after 7 hours contact time.

Application of excess activated sludge ozonation in an SBR Plant. Effects on substrate fractioning and solids production

This paper provides new insights on the application of the ozonation process for the reduction of the activated sludge production in a sequencing batch reactor (SBR). The study was performed in two identical lab-scale SBRs plant, one for experimental activities (Exp SBR) and one used as control (Control SBR), both fed with domestic sewage. A fraction of the activated sludge collected from the Exp SBR at the end of the aerobic react phase was periodically subjected to ozonation for 30 minutes at three different specific dosages (0.05, 0.07 and 0.37 g O(3)/gSS) and then recirculated before the beginning of the following cycle.Recirculation of the ozonated sludge to the Exp SBR did not appreciably affect the efficiency of the biological nitrogen and carbon removal processes. Nonetheless, an improvement of the denitrification kinetic was observed. Mixed liquor volatile and suspended solids (MLSS and MLVSS, respectively) concentrations in the reactor decreased significantly with time for long term application of the ozonation treatment. Kinetic batch tests on unstressed sludge taken from Control SBR indicated that the different oxidant dosages (0.05, 0.07 and 0.37 g O(3)/gSS) and durations of the ozonation process (10, 20 and 30 minutes) used remarkably affected chemical oxygen demand (COD) and organic nitrogen fractioning. In particular, soluble and biodegradable fractions seemed to be higher at lower dosage and longer contact time.

The effect of operating variables on chelant-assisted remediation of contaminated dredged sediment

The paper shows the results from a number of lab-scale washing treatments using the four chelating agents EDTA, NTA, citric acid and [S,S]-EDDS aiming at the remediation of a real heavy metal-contaminated sediment. Investigation of the influence of chelant type and concentration as well as solution pH was the major focus of the work. The analysis of speciation of metals and chelating agents in solution was carried out through geochemical speciation modelling in order to identify the optimal conditions for the washing process as well as to evaluate the competition phenomena of metal-chelant complexes in solution. The major competing cations were found to be Ca above all and Mg under specific conditions. Among the investigated chelating agents, EDDS appeared to be less affected by competition by major cations while ensuring adequate heavy metal extraction efficiencies. For a 1:1 chelant/metal ratio, the following ranking was observed: EDDS>Cit>NTA>EDTA for As, EDDS>NTA congruent withEDTA>>Cit for Cu, EDDS congruent withEDTA congruent withNTA>Cit for Zn, EDTA>NTA>EDDS>Cit for Pb at pH 5 and EDTA congruent withEDDS congruent withNTA>>Cit for Pb at pH 8. For a 10:1 chelant/metal ratio geochemical modelling indicated that at the equilibrium the extracting solutions were dominated by the free form of the chelating agents, indicating the inability of such species to complex trace metals due the strong interactions existing between heavy metal ions and sediment constituents.

Effect of ozonation on sludge reduction in a SBR plant

This paper provides new insights on the application of the ozonation process for the reduction of activated sludge production in a Sequencing Batch Reactor. The study was performed on two identical lab-scale SBRs plant, fed with domestic sewage: a fraction (1/3 of the working volume) of the activated sludge from one reactor (Exp SBR) was periodically subjected to ozonation for 30 minutes at 0.05 g O(3)/gSS and then recirculated before the beginning of the cycle; the other reactor was used as control and therefore managed at the same sludge retention time but without the application of ozonation. The effects of the recirculation of the ozonated sludge to the Exp SBR were evaluated in terms of biological nitrogen and carbon removal efficiencies, Mixed Liquor Volatile and Suspended Solids (MLSS and MLVSS, respectively) concentrations, effluent quality and sludge settleability. Besides, characterization of the ozonated sludge was carried out for different oxidant dosages (0.05, 0.07 and 0.37 g O(3)/gSS) and durations of the ozonation process (10, 20 and 30 minutes). The results show that at 0.05 g O(3)/gSS and 30 minutes contact time MLVSS as well as MLVSS/MLSS ratio do not change appreciably. Ozone dosage must be increased much further to obtain a relevant effect.

A kinetic study of chelant-assisted remediation of contaminated dredged sediment

A study on the remediation of a real heavy metal-contaminated sediment was conducted using the four chelating agents ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), citric acid and the S,S-isomer of the ethylenediaminedisuccinic acid ([S,S]-EDDS). Different chelant washing experiments were carried out at a chelant/total metal content of 1 and 10 mol/mol for treatment durations from 0.5 to 48 h to study the extraction kinetics of trace metals and major cations. The objective was to evaluate the removal efficiency of conventional chelating agents as compared to innovative, biodegradable species. Among the target contaminants, Cd, Cu, Pb and Zn were found to be adequately removed by both EDTA and EDDS, while NTA and citric acid yielded unsatisfactory results in some cases. It was also found that As was a critical contaminant which would require an additional specific treatment step, since the residual concentrations after the washing treatment were still far above the regulatory limit values.

Effect of feed/inoculum ratio on anaerobic digestion of sonicated sludge

In recent years, relevant interest has been devoted to activated sludge disintegration and solubilisation techniques in order to cope with the biological limitations related to particulate degradation. Mechanical disintegration with ultrasound can efficiently transform insoluble organics into a soluble form: the solubilised organic matter is released from the cells to the bulk phase, thus accelerating the hydrolysis step in the digestion process. Experiments were carried out on bench scale anaerobic reactors fed with either untreated or disintegrated excess sludge, added with a biomass inoculum taken from a full scale anaerobic digester. Digestion tests have been carried out at different feed/inoculum ratios (F/I) in the range of 0.1-2, kinetics of VS reduction has been investigated and a beneficial effect of sonication is observed for all the experimental conditions. Similar beneficial results have also been found for biogas production with a maximum gain of 25% at 0.5 F/I ratio.

Influence of anaerobic digestion on particle surface charge and optimal polymer dosage

Anaerobic digestion leads to significant changes of the sludge structural matrix, affecting particle size distribution and dewaterability. The surface charge, determined by means of streaming current, can be effectively used to monitor the complex phenomena of floc disruption, colloid formation and chemical conditioning. To study the relation between surface charge and optimal dosage, two different cationic polyelectrolytes were used: Praestol 644, polymer with high molecular weight and low charge density, and Poly Dadmac, with relatively low molecular weight but high charge density. The optimal Poly Dadmac dosage strictly met the value required to neutralise particle charge whereas the optimal dosage of Praestol 644 indicated that the relevant charge was considerably lower than the one required for charge neutralisation. Mechanisms of action are therefore clearly different. Another objective was to investigate the changes of dewatering characteristics of secondary sludge during anaerobic digestion tests at different inoculum content by determining charge density, and optimal polymer dosage. The optimal polyelectrolyte dosage remains almost constant during digestion at high inoculum, but a significant increase in the first period is observed at low inoculum, thus suggesting that the release of colloidal and supracolloidal material from sludge affects dewaterability, especially in the first days of digestion.

Biological treatment of tannery wastewater in the presence of chromium

Experiments were carried out to determine the feasibility of treating tannery wastewater containing chromium, an inhibiting compound, with sequencing batch reactors (SBR). The maximum chromium concentration tolerated by microorganisms was determined through aerobic and anoxic batch experiments, and the biomass inhibition process was analyzed in a lab scale reactor at increasing chromium concentrations. The results obtained, in batch experiments and in the SBR reactor, have demonstrated that chromium addition had less influence on the denitrification bacteria than on the nitrification bacteria. In addition, it was observed that nitrification and denitrification rates, at the same chromium concentration, were higher in the SBR reactor than in batch experiments with unacclimated biomass. Experimental results confirm that sequencing batch reactors are able to produce a more resistant biomass, which acclimates quickly to inhibiting conditions. A large amount of chromium was found in the sludge from the reactor, while the effluent was devoid of the inhibiting metal.

Experimental study on nitrification in a submerged aerated biofilter

The aim of the present work was to evaluate the performance of a semi-pilot scale BAF in order to obtain a highly polished effluent in terms of removal of organic matter, suspended solids and ammonia and to observe the influence of temperature, pH and nitrite accumulation on the nitrification process. The ammonia removal efficiency during summer and winter and the nitrite accumulation in presence of free ammonia were observed. The biomass density was measured at different filter bed heights and the sludge production from the effluent of the backwashing water was evaluated. The results obtained were used to calibrate a mathematical model for the prediction of the ammonia removal profile in the filter bed and of biomass thickness.

Experimental study on carbon removal in biological aerated filters

The aim of the present work was to evaluate the performance of a pilot-scale BAF in terms of removal of organic matter and suspended solids to obtain a highly polished effluent. The first part of the research was the evaluation of the optimal filter media for a full scale BAF. Mechanical and biological tests were performed over four materials: glass, plastic, pozzolan and expanded clay (Arlita) and the results obtained showed that the plastic spheres and the Arlita particles were the optimal materials for both the mechanical and biological requirements. Hence, a down-flow pilot scale BAF was set up in the laboratory to treat a synthetic medium. As filter media first plastic spheres and then Arlita spheres were used. Carbon removal studies were carried out at several influent COD concentrations, specific removal efficiency and COD profiles along the height of the filter were determined and used to analyze the process. Validation and calibration of a mathematical model formulated for carbon removal, were also performed by using the experimental data obtained. The results showed that this system allows us to achieve the more strict limits on final effluent.

A model to control intermittent aeration phases

Dealing with intermittent aeration as a useful practice to improve nitrogen removal efficiency of activated sludge plants, the possibility to plan optimal temporisation during daytime was investigated. A mathematical model (NIDEN) that allows us to manage different situations, with respect to influent load, environmental conditions and operating strategy, was then developed. The model represents a useful tool especially to plan the aeration cycles in small and medium sized plants, where high costs of automatic control through on-line instrumentation might not be justified. Once the input variables have been defined and the set-point values for tank nutrient concentration have been fixed, NIDEN gives an optimal phase temporisation, to obtain either the maximum energy saving or the best total nitrogen removal.

Aerobic storage by activated sludge on real wastewater

Activated sludge processes are often operated under dynamic conditions, where the microbial response can include, besides of growth, several COD removal mechanisms, and particularly the storage in form of polymers. While abundant evidence of aerobic storage under dynamic conditions with synthetic substrates can be found (Majone et al., Water Sci. Technol. 39(1) (1999) 61), there is still little knowledge about COD removal mechanisms with real activated sludge and wastewater. The aim of the present paper is therefore to give a direct evidence of storage phenomena occurring when a real sludge is mixed with influent wastewater and of their influence onto OUR profiles in typical respirometric batch tests. For this purpose, respirometric batch tests were performed on the same sludge by using acetate, filtered wastewater and raw wastewater as carbon source along with determination of acetate uptake and storage polymer formation. Comparison of results obtained has shown that poly-3-hydroxybutyrate (PHB) storage gives always the main contribution to acetate removal and that in the case of wastewater PHB is also formed from other substrates. PHB formation clearly occurs during the high-rate RBCOD-phase, however for wastewater it accounts for only a fraction (18-22%) of overall RBCOD removal, so calling for other unidentified storage compounds or other non-storage phenomena. In the low-rate SBCOD phase of respirogram PHB is clearly utilised in tests with acetate as internal reserve material once the acetate is depleted. In tests with filtered and raw wastewater the PHB concentration decreases much slower, probably because more PHB is formed due to the availability of external SBCOD (soluble and not). Moreover, reported OUR in the SBCOD-phase from filtered or raw wastewater are quite higher than those reported in batch tests with acetate, so confirming a main contribution of external SBCOD. However, the respective contributions for utilisation of previously stored compounds and of external SBCOD cannot be easily separated by the comparison of tests on filtered and raw wastewater, because both substrates are simultaneously present also in tests with the filtered wastewater. As a side consequence, the chemical-physical method for evaluation of true soluble and biodegradable COD tends to overestimate the respirometry-based RBCOD, at least for the wastewater under observation. Even though modelling by ASM3 (Gujer et al., Water Sci. Technol. 39(1) (1999) 183) makes it possible to well describe the whole experimental behaviour, it requires that much more storage compounds are formed than the experimentally observed PHB. These compounds have still to be identified and quantified in order to confirm the conceptual structure of ASM3.

Kaolinite sorption of Cd, Ni and Cu from landfill leachates: influence of leachate composition

Heavy metal speciation in landfill leachates plays a significant role in determining the mobility during the percolation through soils. The complexation characteristics of landfill leachate directly affects heavy metal solubility and the extent of the interaction with soils, lowering or raising the sorbed amount depending on the relative affinity of the complexed metal and uncomplexed form to soil adsorption sites. In this paper, the adsorption of Cd, Ni and Cu onto kaolinite from three leachates (collected from landfill at different fermentation stage) is studied, also in comparison with metal speciation by two different operative procedures. The heavy metals, at their natural concentration, were divided into operational classes according to an exchange-based procedure and by fractionation on the basis of molecular weight (exchange onto Chelex100 resin and ultrafiltration, respectively). All the experiments were performed also on synthetic solutions designed according to leachate composition and theoretical speciation. The experimental results have shown leachate complexing capacity is strongly dependent on landfill age, and that broad parameters such as COD, DOC, pH, ionic strength and VFA concentration are not able to predict it. It is notheworthy that the strong complexing capacity of leachate can cause extraction of metals from the solid phase instead of adsorption from the liquid one.