Heavy metal removal in MBR systems utilizing insitu adsorption on eggshell

This paper aims to investigate the possibility to combine a MBR (Membrane Biological Reactor) with an adsorption process onto powdered eggshell (PES) and eggshell membrane (ESM) in order to improve metal removal from wastewater (one of the objectives of research project "RES NOVAE, PON04a2_E”). The presence of metals in municipal wastewater is a big source of pollution for water and soil. Toxicity of metals is very dangerous for aquatic life and human health, also when small amount of metals are tolerated by organisms, because of the “biological amplification”, which occurs by food chain. In order to improve water quality, MBR processes could be used. Although MBR processes provide good performances in some metal removal, such as Pb, Cu Ni (about 70%),instead they show a lower efficiency about other species disposal: As, Hg, Zn. In addition metal presence in the MBR influent could increase membrane fouling through scaling and has also a coagulant action on colloidal flocs, inducing the pore blocking phenomena. Metals also induce changes of EPS (Extracellular Polymeric Substance), flocs size and sludge features. In order to improve MBR removal skills, a possible solution is the use of a combined system of a membrane bioreactor together with a lowcost adsorbent: PES and ESM. Their high porosity and surface properties make them able to remove heavy metals, phenolic compounds, dyes and pesticides from wastewater, with further advantages like: low cost, availability and no need for any pretreatment for surface activation. The first step of experimental analysis consists in the evaluation of the compatibility between the two processes: a study about sorbent concentration and size effect on fouling was conducted. The ultrafiltration results, obtained using a submerged hollow fiber PVDF membrane, show that membrane resistance increases with increasing sorbent concentration and decreasing sorbent diameter. The second step concerns the check up of eggshell removal skills as a function of sorbent size, achieved treating an aqueous solution containing Al3+, Fe2+ and Zn2+ as water pollutants. Finally, a synthetic wastewater was treated by three alternative process schemes, : • ALTERNATIVE 1: MBR only; • ALTERNATIVE 2: Two step: Pretreatment units and MBR. • ALTERNATIVE 3: MBR and adsorption process in the same unit. Results, fig.1, demonstrate that the optimization of the Alternative 2 could be a solution to MBR upgrading, because: • Metal removal presents the highest values for each species analyzed; • Permeate flow rate in the MBR shows the highest value; • Sedimentation process improve COD removal; • With adsorption unit located before the bioreactor( s), microorganisms are preserved from inhibition and poisoning; • The settler allows eggshells disposal before they arrive in MBR, reducing membrane fouling and permitting higher eggshell concentration in the adsorption unit; • Easy location in existing plants.