Research experiences on the reuse of industrial waste for concrete production

The aim of this study was to assess the feasibility of concrete production using different kinds of industrial wastes as “recycled aggregate”. The wastes studied in this work were: fly ashes and slags from Electric Arc Furnace (EAF) steel plant; foundry sands produced from foundry dies; slags from lead processing; Waelz slags; solid residues from municipal solid waste incineration (MSWI) plant (with mass-burning kiln and fluidized bed reactor); sludge from industrial wastewater treatment plants. Good compressive strength (similar to natural concrete) was achieved after 28 days of curing by concrete mixtures obtained with the partial replacement (from 7% to 40% by weight) of natural aggregates with slags from lead processing, foundry sands, Waelz slags and bottom ashes from MSW incineration. The worst mechanical and leaching behaviours were shown by concrete samples containing EAF fly ashes and sludge from industrial wastewater treatment. For the residues with the best performance, concrete products (kerbs and flat tiles) were casted. Their mechanical and leaching characterization has shown that the reuse of these residues for concrete product is feasible

Dynamical p-adaptivity for LES of compressible flows in a high order DG framework

We investigate the possibility of reducing the computational burden of LES models by employing locally and dynamically adaptive polynomial degrees in the framework of a high order DG method. A degree adaptation technique especially featured to be effective for LES applications, that was previously developed by the authors and tested in the statically adaptive case, is applied here in a dynamically adaptive fashion. Two significant benchmarks are considered, comparing the results of adaptive and non adaptive simulations. The proposed dynamically adaptive approach allows for a significant reduction of the computational cost of representative LES computation, while allowing to maintain the level of accuracy guaranteed by LES carried out with constant, maximum polynomial degree values

Review of rheological behaviour of sewage sludge and its importance in the management of wastewater treatment plants

Abstract The process operation of wastewater treatment plants (WWTPs) is based on the proper set up of several physical, chemical and biological parameters. Often, issues and problems arising in the process are strictly linked to the rheological behaviour of sewage sludge (SeS). Therefore, rheological measurements, which recently have captured a growing interest, represent an important aspect to consider in the design and operation of WWTPs, especially in the sludge-handling processes. The knowledge of rheological behaviour of SeS represents a crucial step to better understand its flow behaviour and therefore optimize the performance of the processes, minimizing the costs. The SeS are non-Newtonian fluids and, to date, Bingham and Ostwald models are the most applied. This work presents an overview of scientific literature about the rheological properties of SeS and discusses the importance of its knowledge for the management of WWTPs

Why use a thermophilic aerobic membrane reactor for the treatment of industrial wastewater/liquid waste?

This paper describes the advantages of thermophilic aerobic membrane reactor (TAMR) for the treatment of high strength wastewaters. The results were obtained from the monitoring of an industrial and a pilot scale plant. The average chemical oxygen demand (COD) removal yield was equal to 78% with an organic loading rate (OLR) up to 8-10 kgCOD m(-3) d(-1) despite significant scattering of the influent wastewater composition. Total phosphorus (TP) was removed with a rate of 90%, the most important removal mechanism being chemical precipitation (as hydroxyapatite, especially), which is improved by the continuous aeration that promotes phosphorus crystallization. Moreover, surfactants were removed with efficiency between 93% and 97%. Finally, the experimental work showed that thermophilic processes (TPPs) are complementary with respect to mesophilic treatments

Control measures for cyanobacteria and cyanotoxins in drinking water

Algal bloom can represent a serious consequence of the eutrophication of surface water. Some of these algae, called cyanobacteria, are of particular interest for their effect on human health due to their capacity to produce cyanotoxins. In many countries, in fact, there are important problems of poisoning attributed to toxic cyanobacteria and contamination of water sources (specially lakes) resulting in increased cyanobacterial growth. Cyanobacteria can become particularly harmful for humans when water is used for drinking consumption; in fact, they can generate many problems in drinking water treatment plants (increase of solids load, bacterial growth in sand and GAC filters, low efficiency of disinfection) and in the distribution system (growth in reservoir tanks and pipes). Moreover, algal toxins produced by cyanobacteria can be released during water treatment and can persist in water until final consumption. For these reasons, appropriate technologies should be used for water treatment in order to efficiently remove cyanobacteria cells, to reduce the risk of cyanotoxins release and to efficiently remove dissolved toxins. In this work, an overview on the main conventional and advanced processes for Cyanobacteria and Cyanotoxins removal from drinking water will be presented. Moreover, the main results of an experimental research on the removal of Cyanobacteria cells (coagulation/flocculation, sand filtration, GAC filtration, chlorine oxidation) and of cyanotoxins (activated carbon) will be discussed

The reuse of solid residues from mass-burning and fluidized-bed reactors for concrete production

The present work concerns the evaluation of MSWI solid residues reuse as partial replacement of natural aggregates for concrete production. The residues studied are: bottom ash derived from two mass-burning kilns (MB(A) and MB(B)) that treat MSW; exhausted sand and bottom ash derived from a fluidized-bed incinerator (FB(C)) that receive MSW-derived solid recovered fuel (SRF). The bottom ash derived from MB(A) were pre-treated by means sieving and iron removal processes; moreover, additional washing was applied. Sieving and iron removal processes with a subsequent ageing (for two months) were performed on the bottom ash derived from MB(B). Natural aggregate was partially replaced (with a weight percentage from 7% to 40%) with different residues for the production of some concrete mixtures, casted adopting different types or dosages of residues and two different type of cement. Regarding the mechanical characterization of concrete mixtures, the use of 400 kg/m3 (corresponding to 23% of natural aggregate replacement) of bottom ash from fluidized-bed reactor (with the use of CEM42.5R) showed the best results: in this case concrete mixtures could be classified in concrete class C16/20, suitable for structural elements made of reinforced concrete. The results of the leaching test showed that only the washed bottom ash from the mass-burning kiln could be reused following the simplified procedures according to Ministerial Decree 186/2006. For the exhausted sand derived from the fluidized-bed incinerator, the release of some pollutants (especially chromium and arsenic) was higher than the other residues. As concerns the leaching behaviour, concrete mixtures containing the residues derived from fluidized-bed reactor showed a release of pollutants higher than the other mixtures

Oxygen transfer improvement in MBBR process

In the last years, the upgrading of wastewater treatment plants (WWTPs) could be required in order to comply with the more stringent regulation requirements. Nevertheless, the main issue is related to the surface availability. A proper solution could be represented by the attached biomass processes, in particular the moving bed biofilm reactors (MBBR), that have a significant footprint reduction with respect to conventional activated sludge (CAS). However, MBBR showed an important disadvantage: the poor aeration energy efficiency due to the use of coarse bubble diffusers, which guarantee high reliability and low maintenance costs with respect to fine bubble ones. Moreover, the presence of carriers inside the reactor emphasizes this aspect. The aim of this work is to verify the benefits achievable by installing a fine bubble aeration system inside a MBBR system. The comparison, in terms of oxygen transfer efficiency, between a medium bubble aeration system and a fine ceramic bubble diffuser was studied and the effect of biofilm growth on oxygen transfer was assessed. Several tests were carried out in order to test the operation of a coarse and a fine bubble side aeration at different air flow rates, both in clean water conditions, in order to evaluate the influence of carriers (Chip M type) on the aeration efficiency, both in wastewater conditions with the aim to assess the effect of bacteria growth on the carriers. The main results are the following: (i) the fine bubble system placed off-center ensured good mixing even without using the mixer; (ii) the fine bubble side aeration system compared to the coarse ones did not show significant advantages in terms of oxygen transfer efficiency; (iii) the increase in specific air flow rate negatively influenced the aeration efficiency; (iv) the presence of biomass had a positive effect on the oxygen transfer yield

Leaching behaviour of municipal solid waste incineration bottom ash: From granular material to monolithic concrete

The aim of this work was to assess the leaching behaviour of the bottom ash derived from municipal solid waste incineration (MSWI) used in concrete production. In particular, the release of pollutants was evaluated by the application of different leaching tests, both on granular materials and monolithic samples (concrete mixtures cast with bottom ash). The results confirmed that, according to Italian regulations, unwashed bottom ashes present critical issues for the use as alternative aggregates in the construction sector due to the excessive release of pollutants; instead, the leachate from washed bottom ashes was similar to natural aggregates. The concentration of pollutants in the leachate from concrete mixtures was lower than regulation limits for reuse. The crushing process significantly influenced the release of pollutants: this behaviour was due both to the increase in surface area and the release of contaminants from cement. Moreover, the increase in contact time (up to 64 days) involved more heavy metals to be released