Aquacultural approaches to recycling of dissolved nutrients in secondarily treated domestic wastewaters—I Nutrient uptake and release by artificial food chains

Wastewater based artificial food chains composed of sequential monocultures of a suspended unicellular green alga, of an herbivorous cladoceran crustacean, and of an herbivorous or a carnivorous teleost fish and of filamentous green algae were studied in an effort to find efficient, potentially economically viable mechanisms for the biological capture (tertiary treatment) of nutrients (especially nitrate and phosphate) in wastewaters processed by small to medium size two-stage treatment plants that primarily handle domestic and agricultural wastes.All experiments were carried out on laboratory scale systems with a low technology approach to keep apparatus and procedures as simple and reliable as possible.Among all organisms tested as components of the artificial food chains only the unicellular green alga Scenedesmus, the filamentous green algae Cladophora and Ulothrix, the cladoceran crustaceans Daphnia magna and Daphnia pulex, and the teleost fishes Notemigonus crysoleucas, Pimephales promelas and Notropis lutrensis were found to be suitable.Unmodified secondarily treated domestic effluents were both iron deficient and lacking in buffering capacity necessary for optimal algal growth. Additions of both ferrous iron (1 ppm) and carbon dioxide (5%) were required to achieve good quality cultures suitable for feeding cladocerans. Most removal of nutrients occurred in the first algal stage of the food chain. Nitrate removal averaged 78%, phosphate removal 55% in buffered algal cultures. In unbuffered cultures nitrate removal was 30%, phosphate removal 98%. The near complete removal of phosphate in unbuffered algal cultures was probably due to physico-chemical precipitation of phosphate complexes formed as a result of high pH levels (pH > 10) reached within 24 h of culture initiation. Cladoceran and fish stages added nutrients (mostly ammonia and phosphate) back into the effluent. A final stage of Ulothrix and Cladophora algae removed nutrients regenerated by cladocerans and fishes. A 12 h light–12 h dark cycle statistically significantly reduced levels of nutrient removal by both unbuffered and buffered algal cultures below removal rates measured in algae cultured in continuous light. Daily harvesting rates of 25–75% of culture volumes had no significant effect upon removals of nitrate by buffered algal cultures; phosphate removals were inversely proportional to harvesting rates in these cultures.Important theoretical and technical points are discussed.     

The effect of intraperitoneal and intra-aortic chemotherapy for unresectable gastric cancer

Regional chemotherapy was given 16 unresectable gastric cancer patients. Two types of the chemotherapy, intraperitoneal (IP) and intraaortic (IA) administration, were carried out. The control group was comprised of 17 patients. The response of the chemotherapy for primary tumor was 36.4% in the IP group and 20% in the IA one. Among these patients, 2 of 11 in IP and 1 of 5 in IA were able to resect the primary tumor. The 50% survival time of IP, IA and control was 347, 227 and 78 days, respectively. One-year survival rates of IP, IA and control were 68%, 29% and 0%, respectively. IP showed a significantly longer survival rate than controls (p < 0.001). All but one patient was able to stay at home. Intraperitoneal chemotherapy showed both local and systemic effects in unresectable gastric cancer.     

Evaluation of the genotoxicity of stevioside and steviol using six in vitro and one in vivo mutagenicity assays

Stevioside, a constituent of Stevia rebaudiana, is commonly used as a non-caloric sugar substitute in Japan. The genetic toxicities of stevioside and its aglycone, steviol, were examined with seven mutagenicity tests using bacteria (reverse mutation assay, forward mutation assay, umu test and rec assay), cultured mammalian cells (chromosomal aberration test and gene mutation assay) and mice (micronucleus test). Stevioside was not mutagenic in any of the assays examined. The aglycone, steviol, however, produced dose-related positive responses in some mutagenicity tests, i.e. the forward mutation assay using Salmonella typhimurium TM677, the chromosomal aberration test using Chinese hamster lung fibroblast cell line (CHL) and the gene mutation assay using CHL. Metabolic activation systems containing 9000 g supernatant fraction (S9) of liver homogenates prepared from polychlorinated biphenyl or phenobarbital plus 5,6-benzoflavone-pretreated rats were required for mutagenesis and clastogenesis. Steviol was weakly positive in the umu test using S.typhimurium TA1535/pSK1002 either with or without the metabolic activation system. Steviol, even in the presence of the S9 activation system, was negative in other assays, i.e. the reverse mutation assays using S.typhimurium TA97, TA98, TA100, TA102, TA104, TA1535, TA1537 and Escherichia coli WP2 uvrA/pKM101 and the rec-assay using Bacillus subtilis. Steviol was negative in the mouse micronucleus test. The genotoxic risk of steviol to humans is discussed.     

Quantum renormalization group and excitonic phase transition in a strong magnetic field

The critical behavior of excitonic fluctuations is investigated at low temperatures. The Wilson renormalization group is applied to a generalized free-energy functional of the Landau-Ginzburg-Wilson type, which is derived by coarse-graining a microscopic functional. The quantum mechanical effects give rise to an increase of the effective dimensionality at zero temperature. The values of this increase z are z = 1 for a semiconductor and z = 2 for a semimetal, depending on whether the electronic density of states is zero at the Fermi energy or not, respectively. Quantum-classical crossover phenomena appear at a finite but low temperature. As the phase transition point is approached in a semimetal the critical fluctuations in real space first grow two-dimensionally in the plane perpendicular to the magnetic field and then develop three-dimensionally. It is explicitly shown that the mean field theory breaks down in a semiconductor.Correspondence and reprint requests should be addressed to Tatsuzo Nagai.     

Aquacultural approaches to recycling of dissolved nutrients in secondarily treated domestic wastewaters-II biological productivity of artificial food chains

We have studied the biological productivity, measured as biomass yields, of laboratory scale artificial food chains composed of sequential monocultures of suspended unicellular green algae (Scenedesmus), herbivorous cladoceran crustaceans (Daphnia magna), and herbivorous teleost fish (Hypophthalmichthys). These food chains were grown in minimally modified secondarily treated, chlorinated then dechlorinated, domestic waste waters. Successive stages in the chains were fed the organisms grown in the just preceding stages.Additions of 1 ppm ferrous sulfate and aeration with mixtures of air plus 5% carbon dioxide (buffered cultures) increased yields of Scenedesmus cultures by 52% above yields of air aerated, unsupplemented cultures (unbuffered cultures). Buffered cultures remained stable for long periods (1–2 weeks) and maintained good cell quality (no chlorosis; 90+% of cells present were Scenedesmus). Unbuffered, unsupplemented cultures soon became chlorotic, cells autoflocculated (which greatly reduced yields), and changes occurred in species composition. These latter cultures were unsuitable as food for cladocerans.Three production indices (conversion coefficients, specific production, and production/biomass ratios) showed that better growth occurred in cladoceran cultures fed buffered algal cultures as compared with unbuffered cultures. When fed unbuffered cultures cladocerans showed higher production indices when flocculated but unsettled cultures were used, as compared with supernates from flocculated, settled cultures.Attempts to grow the primarily herbivorous silver carp (Hypophthalmichthys molitrix) in a two-stage (buffered algae-fish) food chain failed. Ammonia toxicity may have been the cause of fish deaths.     

Human late-receptor potential and its clinical use in dyschromatopsia

The off response of the P III component isolated by aspartate in the human eyecup in vitro showed an initial rapid decay followed by a slow decay. The rapid decay in the human ERG originates mainly in cones. The rapid decay was also observed in human subjects. The spectral sensitivity curve of the rapid decay was found to be shifted toward short wavelengths in all nine protanopes tested. In these cases of protanopia, anomalous cone functions were indicated.     

Delayed failure in silica glass

Stable crack-propagation behaviour in silica glass as a raw material for optical fibres is studied under static tensile stress in various environments such as distilled water, NaCl aqueous solution, air and dry nitrogen gas, and the influence of these environments is discussed. The crack-growth rate in distilled water is obtained qualitatively as a function of the stress intensity factor and temperature, and the activation energy of the cracking process is determined as 97.6 kcal mol^–1. The growth rate seems to be unaffected by Na⁺ and Cl^– ions in an NaCl acqueous solution, but is influenced significantly by the humidity in the atmosphere. In a dry atmosphere, the growth rate in Region II cannot be expressed as a single function of the stress intensity factor. A plot of the log of time to failure against the initial stress intensity factor reveals a linear relationship in the environments tested. The critical fracture stress of an optical fibre is evaluated taking account of the crack size on the basis of fracture mechanics concept.