ABSTRACT
The toxicity of leather tanning wastewater from a traditional tannery (TT), which is based on vegetable tannin (VT), was compared with wastewater from a tannery combining the use of chromium-based tanning (CT) with VT-based tanning operations. Wastewater samples from a TT and a CT plant as well as from five sewer sampling points were collected in Marrakesh, Morocco, and the concentrations of VT and some selected inorganics were measured. A set of bioassays were used to test wastewater toxicity in sea urchin (Paracentrotus lividus) embryos and sperm, in Daphnia magna, and in marine microalgae (Dunaliella tertiolecta). Toxicity end points included: (1) developmental defects, embryonic mortality, sperm fertilization success, and offspring damage in sea urchins; (2) D. magna immobilization; and (3) algal growth rate inhibition. Toxicity tests on TT and CT effluents (TTE and CTE) were run at dilutions ranging from 0.1% to 2% (sea urchins and algae) or up to 12% in D. magna. Parallel bioassays were run on VT extract (VTE) at nominal tannin concentrations ranging from 0.1 to 10 mg l(-1). The results showed higher toxicity of CTE compared with TTE. CTE toxicity in sea urchins and algae showed concentration-related trends, whereas TTE exerted hormetic effects at levels of 0.1% to 0.2% and toxic effects at levels >or=1%. The same trends were observed for VTE, suggesting a prevailing role of tannin in TTE-associated effects. The moderate wastewater toxicity of VT-based tanneries might prompt interest in the VT tanning process.
Subject(s)
Chromium/toxicity , Tanning , Tannins/toxicity , Waste Disposal, Fluid , Water Pollutants, Chemical/toxicity , Animals , Biological Assay , Daphnia/drug effects , Daphnia/physiology , Embryo, Nonmammalian/drug effects , Eukaryota/drug effects , Eukaryota/growth & development , Female , Male , Sea Urchins/embryologyABSTRACT
P-control technologies for municipal wastewater are essentially based on "destructive" methods, that lead to formation of concentrated solid-phases (sludge), usually disposed-off in controlled landfills. Ion exchange, as a "non-destructive" technology, allows for selective removal and simultaneous recovery of pollutants, which can be recycled to the same and/or related productive lines. In this context, the REM NUT process removes nutrient species (HPO4 = , NH4+, K+) present in biologically oxidised municipal effluents and recovers them in the form of struvites (MgNH4PO4; MgKPO4), premium quality slow release fertilisers. The main limitation to the extensive application of this ion exchange based process is the non-availability of selective exchangers for specific removal of nutrient species. This paper illustrates laboratory investigation and pilot scale development of a so-called "P-driven" modified REM NUT scheme based on a new phosphate-selective sorbent developed at Lehigh University, PA, USA.
Subject(s)
Phosphorus/isolation & purification , Waste Disposal, Fluid/methods , Adsorption , Conservation of Natural Resources , Fertilizers , Magnesium Compounds/chemistry , Phosphates/chemistry , Phosphates/isolation & purification , Sewage/chemistry , StruviteABSTRACT
Nutrients control technologies from wastewater are based on destructive technologies which defer the problem fromthe diluted liquid-phase (effluent) to a more concentrated waste (sludge) in the case of phosphates, or to nitrogen gas and/or volatile compounds in the case of ammonia. The REM NUT process allows for simultaneous removal of phosphate and ammonium ions by selective ion exchange and recovery by chemical precipitation in the form of struvite (magnesium ammonium phosphate) from the spent exchangers regeneration eluates. In the paper revised versions of the REM NUT process, i.e., P-driven layouts, are presented and cost effectiveness is compared to chemical precipitation based on the use of ferric chloride.
