Acque del Chiampo SpA

Arzignano, Italy

Acque del Chiampo SpA

Arzignano, Italy
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Bertani R.,University of Padua | Biasin A.,University of Padua | Canu P.,University of Padua | Della Zassa M.,University of Padua | And 3 more authors.
Journal of Hazardous Materials | Year: 2016

Similarly to many powders of solids, dried sludge originated from tannery wastewater may result in a self-heating process, under given circumstances. In most cases, it causes a moderate heating (reaching 70-90. °C), but larger, off-design residence times in the drier, in a suboxic atmosphere, extremely reactive solids can be produced. Tannery waste contains several chemicals that mostly end up in the wastewater treatment sludge. Unexpected and uncontrolled self heating could lead to a combustion and even to environmental problems. Elaborating on previous studies, with the addition of several analytical determinations, before and after the self-heating, we attempted to formulate a mechanism for the onset of heating. We demonstrated that the system Fe/S/O has been involved in the process. We proved that the formation of small quantities of pyrophoric iron sulfides is the key. They are converted to sulfated by reaction with water and oxygen with exothermic processes. The pyrite/pyrrhotite production depends on the sludge drying process. The oxidation of sulfides to oxides and sulfates through exothermic steps, reasonably catalyzed by metals in the sludge, occurs preferentially in a moist environment. The mechanism has been proved by reproducing in the laboratory prolonged heating under anoxic/suboxic atmosphere. © 2015 Elsevier B.V.


Della Zassa M.,University of Padua | Biasin A.,University of Padua | Zerlottin M.,Acque del Chiampo SpA | Refosco D.,Acque del Chiampo SpA | Canu P.,University of Padua
Waste Management | Year: 2013

We studied the reactivity of dried sludge produced by treatment of wastewater, mainly from tanneries. The solids transformations have been first characterized with thermal analysis (TGA and DSC) proving that exothermic transformation takes place at fairly low temperature, before the total organic combustion that occurs in air above 400 °C. The onset of low temperature reactions depends on the heating rate and it can be below 100 °C at very small heating rate. Then, we reproducibly determined the conditions to trigger dried sludge self-heating at the laboratory scale, on samples in the 0.2-0.3. kg size. Thermal insulation, some aeration and addition of water are key factors. Mastering the self-heating at this scale allows more detailed investigations as well as manipulation of conditions, to understand its nature, course and remediation. Here we report proves and discussions on the role of air, water, particle size, porosity and biological activity, as well as proving that also dried sludge from similar sources lead to self-heating. Tests demonstrate that air and water are simultaneously required for significant self-heating to occur. They act in diverging directions, both triggering the onset of the reactions and damping the temperature rise, by supporting heat loss. The higher the O2 concentration, the higher the solids heating rate. More added water prolongs the exothermic phase. Further additions of water can reactivate the material. Water emphasizes the exothermic processes, but it is not sufficient to start it in an air-free atmosphere. The initial solid moisture concentration (between 8% and 15%) affects the onset of self-heating as intuitive. The sludge particles size strongly determines the strength and extent of the heat release, indicating that surface reactions are taking place. In pelletized particles, limitations to water and air permeability mitigates the reaction course. © 2013 Elsevier Ltd.


Zerlottin M.,Acque del Chiampo SpA | Refosco D.,Acque del Chiampo SpA | Della Zassa M.,University of Padua | Biasin A.,University of Padua | Canu P.,University of Padua
Waste Management | Year: 2013

We experimentally studied the occurrence of spontaneous self-heating of sludge after drying, to understand its nature, course and remediation. The sludge originates from primary and biological treatment of both municipal and industrial wastewater, the latter largely dominant (approx. 90% total organic carbon, mainly from local tanneries). Dried sludge is collected into big-bags (approx. 1.5m3) and landfilled in a dedicated site. After several years of regular operation of the landfill, without any management or environmental issue, indications of local warming emerged, together with smoke and smelling emissions, and local subsidence. During a two year monitoring activity, temperatures locally as high as 80°C have been detected, 6-10m deep. Experiments were carried out on large quantities of dried sludge (∼1t), monitoring the temperature of the samples over long periods of time (months), aiming to reproduce the spontaneous self-heating, under different conditions, to spot enhancing and damping factors. Results demonstrate that air is a key factor to trigger and modulate the self-heating. Water, in addition to air, supports and emphasizes the heating. Unusual drying operation was found to affect dramatically the self-heating activity, up to spontaneous combustion, while ordinary drying conditions yield a sludge with a moderate self-heating inclination. Temperature values as well as heating time scales suggest that the exothermic process nature is mainly chemical and physical, while microbiological activity might be a co-factor. © 2012 Elsevier Ltd.


Zassa M.D.,University of Padua | Zerlottin M.,Acque del Chiampo S.p.A. | Refosco D.,Acque del Chiampo S.p.A. | Santomaso A.C.,University of Padua | Canu P.,University of Padua
CHoPS 2015 - 8th International Conference for Conveying and Handling of Particulate Solids | Year: 2015

In this work we quantitatively studied the opportunities to improve the compaction of dried wastewater treatment sludges from tanneries, possibly combining with pelletization. Measurements of bulk density have been carried out at the industrial and laboratory scale, using different packing procedures, amenable to industrial processes. Waste as powder, pellets and their mixtures have been considered. Mixtures of powder and pellets is the best packing policy. The best compaction results was achieved by controlled vibration of a 30/70%wt mixture of powders and pellets, leading to a final bulk density of 1 t/m3, i.e. an improvement of compaction by more than 54% with respect to poured powders, but also larger than 35% compared to poured pellets. That means increasing the mass storage capacity by a factor of 1.56.


Della Zassa M.,University of Padua | Zerlottin M.,Acque del Chiampo S.p.A. | Refosco D.,Acque del Chiampo S.p.A. | Santomaso A.C.,University of Padua | Canu P.,University of Padua
Waste Management | Year: 2015

We quantitatively studied the advantages of improving the compaction of a powder waste by several techniques, including its pelletization. The goal is increasing the mass storage capacity in a given storage volume, and reducing the permeability of air and moisture, that may trigger exothermic spontaneous reactions in organic waste, particularly as powders. The study is based on dried sludges from a wastewater treatment, mainly from tanneries, but the indications are valid and useful for any waste in the form of powder, suitable to pelletization. Measurements of bulk density have been carried out at the industrial and laboratory scale, using different packing procedures, amenable to industrial processes. Waste as powder, pellets and their mixtures have been considered. The bulk density of waste as powder increases from 0.64t/m3 (simply poured) to 0.74t/m3 (tapped) and finally to 0.82t/m3 by a suitable, yet simple, packing procedure that we called dispersion filling, with a net gain of 28% in the compaction by simply modifying the collection procedure. Pelletization increases compaction by definition, but the packing of pellets is relatively coarse. Some increase in bulk density of pellets can be achieved by tapping; vibration and dispersion filling are not efficient with pellets. Mixtures of powder and pellets is the optimal packing policy. The best compaction result was achieved by controlled vibration of a 30/70wt% mixture of powders and pellets, leading to a final bulk density of 1t/m3, i.e. an improvement of compaction by more than 54% with respect to simply poured powders, but also larger than 35% compared to just pellets. That means increasing the mass storage capacity by a factor of 1.56. Interestingly, vibration can be the most or the least effective procedure to improve compaction of mixtures, depending on characteristics of vibration. The optimal packing (30/70wt% powders/pellets) proved to effectively mitigate the onset of smouldering, leading to self-heating, according to standard tests, whereas the pure pelletization totally removes the self-heating hazard. © 2015 Elsevier Ltd.


Biasin A.,University of Padua | Della Zassa M.,University of Padua | Zerlottin M.,Acque del Chiampo SpA | Refosco D.,Acque del Chiampo SpA | And 2 more authors.
Waste Management | Year: 2014

We studied the spontaneous heating of dried sludge produced by treating wastewater mainly originating from tanneries. Heating up to burning has been observed in the presence of air and moisture, starting at ambient temperature. To understand and prevent the process we combined chemical and morphological analyses (ESEM) with thermal activity monitoring in insulated vessels. Selective additions of chemicals, either to amplify or depress the reactivity, have been used to investigate and identify both the chemical mechanism causing the sludge self-heating, and a prevention or a mitigation strategy. FeS additions accelerate the onset of reactivity, while S sustains it over time. On the contrary, Ca(OH)2, Na2CO3, NaHCO3, FeCl2, EDTA, NaClO can limit, up to completely preventing, the exothermic activity. All the experimental evidences show that the reactions supporting the dried sludge self-heating involve the Fe/S/O system. The total suppression of the reactivity requires amounts of additives that are industrially incompatible with waste reduction and economics. The best prevention requires reduction or removal of S and Fe from the dried solid matrix. © 2014 Elsevier Ltd.


PubMed | University of Padua and Acque del Chiampo S.p.A.
Type: | Journal: Waste management (New York, N.Y.) | Year: 2015

We quantitatively studied the advantages of improving the compaction of a powder waste by several techniques, including its pelletization. The goal is increasing the mass storage capacity in a given storage volume, and reducing the permeability of air and moisture, that may trigger exothermic spontaneous reactions in organic waste, particularly as powders. The study is based on dried sludges from a wastewater treatment, mainly from tanneries, but the indications are valid and useful for any waste in the form of powder, suitable to pelletization. Measurements of bulk density have been carried out at the industrial and laboratory scale, using different packing procedures, amenable to industrial processes. Waste as powder, pellets and their mixtures have been considered. The bulk density of waste as powder increases from 0.64 t/m(3) (simply poured) to 0.74 t/m(3) (tapped) and finally to 0.82 t/m(3) by a suitable, yet simple, packing procedure that we called dispersion filling, with a net gain of 28% in the compaction by simply modifying the collection procedure. Pelletization increases compaction by definition, but the packing of pellets is relatively coarse. Some increase in bulk density of pellets can be achieved by tapping; vibration and dispersion filling are not efficient with pellets. Mixtures of powder and pellets is the optimal packing policy. The best compaction result was achieved by controlled vibration of a 30/70 wt% mixture of powders and pellets, leading to a final bulk density of 1t/m(3), i.e. an improvement of compaction by more than 54% with respect to simply poured powders, but also larger than 35% compared to just pellets. That means increasing the mass storage capacity by a factor of 1.56. Interestingly, vibration can be the most or the least effective procedure to improve compaction of mixtures, depending on characteristics of vibration. The optimal packing (30/70 wt% powders/pellets) proved to effectively mitigate the onset of smouldering, leading to self-heating, according to standard tests, whereas the pure pelletization totally removes the self-heating hazard.


PubMed | Acque del Chiampo SpA
Type: Journal Article | Journal: Waste management (New York, N.Y.) | Year: 2012

We experimentally studied the occurrence of spontaneous self-heating of sludge after drying, to understand its nature, course and remediation. The sludge originates from primary and biological treatment of both municipal and industrial wastewater, the latter largely dominant (approx. 90% total organic carbon, mainly from local tanneries). Dried sludge is collected into big-bags (approx. 1.5m(3)) and landfilled in a dedicated site. After several years of regular operation of the landfill, without any management or environmental issue, indications of local warming emerged, together with smoke and smelling emissions, and local subsidence. During a two year monitoring activity, temperatures locally as high as 80C have been detected, 6-10 m deep. Experiments were carried out on large quantities of dried sludge ( 1t), monitoring the temperature of the samples over long periods of time (months), aiming to reproduce the spontaneous self-heating, under different conditions, to spot enhancing and damping factors. Results demonstrate that air is a key factor to trigger and modulate the self-heating. Water, in addition to air, supports and emphasizes the heating. Unusual drying operation was found to affect dramatically the self-heating activity, up to spontaneous combustion, while ordinary drying conditions yield a sludge with a moderate self-heating inclination. Temperature values as well as heating time scales suggest that the exothermic process nature is mainly chemical and physical, while microbiological activity might be a co-factor.

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