Cost minimization in a full-scale conventional wastewater treatment plant: associated costs of biological energy consumption versus sludge production.

Energy consumption and sludge production minimization represent rising challenges for wastewater treatment plants (WWTPs). The goal of this study is to investigate how energy is consumed throughout the whole plant and how operating conditions affect this energy demand. A WWTP based on the activated sludge process was selected as a case study. Simulations were performed using a pre-compiled model implemented in GPS-X simulation software. Model validation was carried out by comparing experimental and modeling data of the dynamic behavior of the mixed liquor suspended solids (MLSS) concentration and nitrogen compounds concentration, energy consumption for aeration, mixing and sludge treatment and annual sludge production over a three year exercise. In this plant, the energy required for bioreactor aeration was calculated at approximately 44% of the total energy demand. A cost optimization strategy was applied by varying the MLSS concentrations (from 1 to 8 gTSS/L) while recording energy consumption, sludge production and effluent quality. An increase of MLSS led to an increase of the oxygen requirement for biomass aeration, but it also reduced total sludge production. Results permit identification of a key MLSS concentration allowing identification of the best compromise between levels of treatment required, biological energy demand and sludge production while minimizing the overall costs.

Cytotoxicity of copper and cobalt complexes of furfural semicarbazone and thiosemicarbazone derivatives in murine and human tumor cell lines.

The 2-furfural semicarbazone and thiosemicarbazone copper and cobalt complexes demonstrated potent cytotoxicity against the growth of suspended leukemias and lymphomas as well as human lung MB9812, colon SW480, ovary 1-A9 and HeLa-S3 uterine carcinoma. In L1210 lymphoid leukemia cell the complexes inhibited preferentially DNA synthesis over 60 min at 25 to 100 microM. The copper and cobalt complexes functioned by multiple mechanisms to suppress synthetic steps in nucleic acid metabolism to reduce deoxynucleotide pools for incorporation into DNA. At high concentrations the complexes suppressed human DNA topoisomerase II activity with DNA nicks and DNA fragmentation but they did not alkylate the bases of DNA, cause intercalation between base pairs or cause cross-linking of DNA strands.

Stability, toxicity and cytotoxicity of a cupric complex towards cultured CaCo-2 cells.

The human colon adenocarcinoma-derived cell line CaCo-2 was used as a model system to study the effects of copper (II), tetradentate N-alkyl ligand (H2L) and their complex. The stimulatory effect of the complex was obtained with lower concentrations from 10(-7) to 10(-17) mol.L-1, while inhibiting effects occur from 10(-4) to 10(-6) mol.L-1. According to this study, copper (II) and free ligand were toxic for cultured cells. Our data suggested that the complex, according to our toxicity assays in mice, could be used as an antimitotic agent.

Variations in the amino acid composition of cyanophycin in the cyanobacterium Synechocystis sp. PCC 6308 as a function of growth conditions.

Gas chromatography-mass spectrometry studies of the nitrogen isotopic composition of the N-trifluoroacetyl n-butyl ester derivatives of the amino acids from isolated hydrolyzed cyanophycin from 15N-enriched cells led to two major findings: (1) the amino acid composition of this granular polypeptide, isolated using procedures optimized for extracting and purifying cyanophycin from cells in the stationary growth phase, varied with the culture growth condition; (2) the rate of incorporation of exogenous nitrate differed for each nitrogen atom of the amino acid constituents of cyanophycin or cyanophycin-like polypeptide. Arginine and aspartic acid were the principle components of cyanophycin isolated from exponentially growing cells and from light-limited stationary phase cells, with glutamic acid as an additional minor component. The cyanophycin-like polypeptide from nitrogen-limited cells contained only aspartic and glutamic acids, but no arginine. The glutamic acid content decreased and arginine content increased as nitrate was provided to nitrogen-limited cells. These cells rapidly incorporated nitrate at different rates at each cyanophycin nitrogen site: guanidino nitrogens of arginine > aspartic acid > alpha-amino nitrogen of arginine > glutamic acid. Little media-derived nitrogen was incorporated into cyanophycin of exponentially growing cells during one cellular doubling time.