ABSTRACT
Pharmaceuticals and heavy metals pose significant risks to human health and aquatic ecosystems, necessitating their removal from water and wastewater. A promising alternative for this purpose involves their removal by adsorption on composite sorbents prepared using a conventional layer-by-layer (LbL) method or an innovative coacervate direct deposition approach. In this study, four novel composite materials based on a silica core (IS) and a polyelectrolyte coacervate shell were used for the investigation of dynamic adsorption of three heavy metals (lead, nickel and cadmium) and an organic drug model (diclofenac sodium salt, DCF-Na). The four types of composite sorbents were tested for the first time in dynamic conditions (columns with continuous flow), and the column conditions were similar to those used in wastewater treatment plants. The influence of the polyanion nature (poly(acrylic acid) (PAA) vs. poly(sodium methacrylate) (PMAA)), maintaining a constant poly(ethyleneimine) (PEI), and the cross-linking degree (r = 0.1 and r = 1.0) of PEI chains on the immobilization of these pollutants (inorganic vs. organic) on the same type of composite was also studied. The experiments involved both single- and multi-component aqueous solutions. The kinetics of the dynamic adsorption process were examined using two non-linear models: the Thomas and Yoon-Nelson models. The tested sorbents demonstrated good adsorption capacities with affinities for the metal ions in the following order: Pb2+ > Cd2+ > Ni2+. An increase in the initial diclofenac sodium concentration led to an enhanced adsorption capacity of the IS/(PEI-PAA)c-r1 sorbent. The calculated sorption capacities were in good agreement with the adsorption capacity predicted by the Thomas and Yoon-Nelson models. The substantial affinity observed between DCF-Na and a column containing composite microparticles saturated with heavy metal ions was explained.
ABSTRACT
The typical treatment scheme of a large municipal wastewater treatment plant (LWWTP) is almost always the result of design based on technical and economic criteria. Once a threshold in terms of population equivalent (PE) is reached, it is possible that additional sludge thermal treatment might be required. Aspects such as greenhouse gas (GHG) emissions and land use for the construction of the WWTP or the service landfill are considered marginal in current design practice; in a world that requires increasingly attention to the environment, these criteria cannot be ignored when defining the treatment scheme of a LWWTP. With the intent of providing a sustainable approach to design, this study aims to identify the best treatment scheme for a LWWTP with a 720,000 PE size. Methodologically, the study involves the development of an approach based on multi-criteria decision analysis (MCDA). Six alternative treatment schemes were considered; two simplified schemes, without primary sedimentation, with extended aeration activated sludge processes and aerobic sludge stabilization; four full schemes, with primary sedimentation and anaerobic sludge digestion. Some schemes differ for the organic loading rate applied; others for the use of sludge incineration. Subsequently, six evaluation criteria (ECs) such as GHG emissions, electricity consumption, running costs, WWTP planimetric area, surface for the service landfill, as well as WWTP as biorefinery have been considered. The weighting of the ECs involved the participation of the main stakeholders in such a decision-making process, following a bottom-up approach. The resolution of the MCDA problem allowed the identification of the full scheme based on primary sedimentation, biological activated sludge at low organic load (0.210 kgBOD5/kgVSS/d) and anaerobic sludge digestion as the best solution. The sensitivity analysis, able to indirectly take into account the multitude of decision makers involved, allowed corroborating the results. The obtained treatment scheme was different from that generally adopted in current design practice for LWWTPs.
