Microalgae cultivation and culture medium recycling by a two-stage cultivation system

Nutrients and water play an important role in microalgae cultivation. Using wastewater as a culture medium is a promising alternative to recycle nutrients and water, and for further developing microalgae-based products. In the present study, two species of microalgae, Chlorella sp. (high ammonia nitrogen tolerance) and Spirulina platensis (S. platensis, high growth rate), were cultured by using poultry wastewater through a two-stage cultivation system for algal biomass production. Ultrafiltration (UF) or centrifuge was used to harvest Chlorella sp. from the first cultivation stage and to recycle culture medium for S. platensis growth in the second cultivation stage. Results showed the two-stage cultivation system produced high microalgae biomass including 0.39 g·L^–1Chlorella sp. and 3.45 g·L^–1S. platensis in the first-stage and second-stage, respectively. In addition, the removal efficiencies of NH₄⁺ reached 19% and almost 100% in the first and the second stage, respectively. Total phosphorus (TP) removal reached 17% and 83%, and total organic carbon (TOC) removal reached 55% and 72% in the first and the second stage, respectively. UF and centrifuge can recycle 96.8% and 100% water, respectively. This study provides a new method for the combined of pure microalgae cultivation and wastewater treatment with culture medium recycling.

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Mixed culture of <Emphasis Type="Italic">Chlorella</Emphasis> sp. and wastewater wild algae for enhanced biomass and lipid accumulation in artificial wastewater medium

The purpose of this work is to study the co-cultivation of Chlorella sp. and wastewater wild algae under different cultivation conditions (i.e. CO₂, light intensity, cultivation time, and inoculation ratio) for enhanced algal biomass and lipid productivity in wastewater medium using Response Surface Methodology (RSM). The results show that mixed cultures of Chlorella sp. and wastewater wild algae increase biomass and lipid yield. Additionally, findings indicate that CO₂, light intensity and cultivation time significantly affect algal productivity. Furthermore, CO₂ concentration and light intensity, and CO₂ concentration and algal composition, have an interactive effect on biomass productivity. Under different cultivation conditions, the response of algal biomass, cell count, and lipid productivity ranges from 2.5 to 10.2 mg/mL, 1.1 × 10⁶ to 8.2 × 10⁸ cells/mL, and 1.1 × 10¹² to 6.8 × 10¹² total fluorescent units/mL, respectively. The optimum conditions for simultaneous biomass and lipid accumulation are 3.6% of CO₂ (v/v), 160 µmol/m²/s of light intensity, 1.6/2.4 of inoculation ratio (wastewater-algae/Chlorella), and 8.3 days of cultivation time. The optimal productivity is 9.8 (g/L) for dry biomass, 8.6 E + 08 (cells/mL) for cell count, and 6.8 E + 12 (Total FL units per mL) for lipid yield, achieving up to four times, eight times, and seven times higher productivity compared to nonoptimized conditions. Provided is a supportive methodology to improve mixed algal culture for bioenergy feedstock generation and to optimize cultivation conditions in complex wastewater environments. This work is an important step forward in the development of sustainable large-scale algae cultivation for cost-efficient generation of biofuel.

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Free-living marine nematodes from Biscayne Bay,Florida, II. Oncholaimidae: descriptions of five new species and one new genus (Meyersia)

A new genus, Meyersia, and five new species of the nematode family Oncholaimidae, are described from Biscayne Bay, Florida, and environs, viz., Metoncholaimus pelor n. sp., M. amplus n. sp., Meyersia major n. gen., n. sp., M. minor n. sp., and Filoncholaimus prolatus n. sp. Also included in the genus Meyersia are Adoncholaimus bandaenis Kreis, 1932 and A. meridionalis Kreis, 1932.     

Formation of disinfection byproducts from accumulated soluble products of oleaginous microalga after chlorination

When microalgae are simultaneously applied for wastewater treatment and lipid production, soluble algal products (SAP) should be paid much attention, as they are important precursors for formation of disinfection byproducts (DBPs), which have potential risks for human health. Chlorella sp. HQ is an oleaginous microalga that can generate SAP during growth, especially in the exponential phase. This study investigated the contribution of SAP from Chlorella sp. HQ to DBP formation after chlorination. The predominant DBP precursors from SAP were identified with the 3D excitation-emission matrix fluorescence. After chlorination, a significant reduction was observed in the fluorescence intensity of five specific fluorescence regions, particularly aromatic proteins and soluble microbial by-product-like regions, accompanied with slight shifting of the peak. The produced DBPs were demonstrated to include trihalomethanes and haloacetic acids. As the algal cultivation time was extended in wastewater, the accumulated SAP strengthened the formation of DBPs. The trend for DBP formation was as follows: chloroform>dichloroacetic acid>trichloroacetic acid.

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Free-living marine nematodes from Biscayne Bay,Florida, I. Comesomatidae: the male of Laimella longicauda Cobb, 1920, and description of Actarjania new genus

The male of Laimella longicauda Cobb, 1920 is described as having short arcuate spicules and a gubernaculum with caudally directed apophyses. The genus Paracomesoma Schuurmans Stekhoven, 1950 is reinstated to accommodate species of Laimella sensu Chitwood, 1937. Paramesonchium n. gen. is proposed to accommodate Laimella (?) serialis Wieser, 1954. Actarjania n. gen. (type species A. splendens n. sp.) differs from Sabatieria in having irregular lateral rows of longitudinal punctations and short arcuate spicules with distinctive distal extremities.     

A systematic study of some Black Corals species (Antipatharia,Hexacorallia) based on rDNA internal transcribed spacers sequences

A phylogenetic analysis based on rDNA internal transcribed spacers (ITS) sequences was performed on 15 species of black corals assigned to the genera Antipathes, Stichopathes, Cirrhipathes, Rhipidipathes, Antipathella, Myriopathes and Cupressopathes recorded from the Messina Strait (Mediterranean Sea) and the Bunaken Marine Park (Celebes Sea, Indonesia). The phylogenetic analysis shows that the examined species are grouped in two main branches corresponding to the families Antipathidae-Aphanipathidae and Myriopathidae. While among the Myriopathidae species there is a very small genetic distance, the Antipathidae-Aphanipathidae clade shows a high degree of divergence between different genera. According to this study, the taxon Antipathes? sp. 3 characterised by a bush-like corallum without a well-defined axis, probably belongs to a new undescribed genus of the family Antipathidae.     

Physiological adaptations of the invasive cordgrass<Emphasis Type="Italic"> Spartina anglica</Emphasis> to reducing sediments: rhizome metabolic gas fluxes and enhanced O<Subscript>2</Subscript> and H<Subscript>2</Subscript>S transport

Cordgrasses of the genus Spartina form dense monospecific stands worldwide, profoundly influencing the ecology of estuaries. One species, Spartina anglica, originated by allopolyploidy in the 1800s and has been particularly prolific as an invasive species worldwide. S. anglica tolerates low-lying estuarine mudflats that its progenitor species and other coastal halophytes cannot. However, very little is known of the physiology of S. anglica. In the present study, an automated flow-through respirometry system was used to quantify metabolic gas fluxes (O₂, H₂S, CO₂, and NH₃) of S. anglica rhizomes. Enhanced physiological mechanisms to transport O₂ and H₂S in both directions between the rhizosphere and the atmosphere were exhibited by S. anglica, but not by the native North American species S. alterniflora. These results suggest that tolerance of anoxia and H₂S may assist S. anglica in colonizing extensively flooded environments. Enhanced sediment oxygenation by S. anglica may be potentially useful for phytoremediation of contaminated sediments, since microbial degradation of organic pollutants is often limited by O₂ availability.     

HCHs and DDTs in Yellow River of Henan section—a typical agricultural area in China: levels,distributions and risks

The levels, potential sources and ecological risks of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in Yellow River of Henan section, a typical agricultural area in China, were investigated. Surface water samples and suspended particulate matters (SPMs) were collected from 23 sites during two seasons. In wet season, the residues of ∑HCHs (α-HCH, β-HCH, γ-HCH and δ-HCH) and ∑DDTs (p,p′-DDT, o,p′-DDT, p,p′-DDE, p,p′-DDD) ranged from 41.7 to 290 and 4.42 to 269 ng/L in surface water, while those varied from 0.86 to 157 and 1.79 to 96.1 ng/g dw in SPM, respectively. Moreover, in surface water, the levels of HCHs and DDTs in wet season were much higher than those in dry season. The reverse was true for residues of HCHs and DDTs in SPM. Compared with the large rivers in other regions, the levels of HCHs and DDTs in the studied area ranked at high levels and the residual concentrations might cause adverse biological risk, especially for ∑HCHs during wet season. Distributions of HCHs and DDTs delineated that the input of tributaries made a significant effect on the residue of HCHs and DDTs in the mainstream. ∑HCHs in surface water were consist of 26.7 % α-HCH, 30.0 % β-HCH, 37.9 % γ-HCH and 5.45 % δ-HCH and those in SPM contained 5.16 % α-HCH, 22.1 % β-HCH, 60.5 % γ-HCH and 12.2 % δ-HCH on average. Combined with ratios of α-HCH/γ-HCH in surface water (0.70) and in SPM (0.09), the results strongly indicated that lindane was recently used or discharged in the studied area. The mean percentage of DDTs′ isomers were 28.7 % p,p′-DDT, 29.8 % o,p′-DDT, 28.1 % p,p′-DDE and 13.4 % p,p′-DDD in surface water, while those were 12.5 % p,p′-DDT, 31.8 % o,p′-DDT, 30.5 % p,p′-DDE and 25.1 % p,p′-DDD in SPM. The ratios of (DDE + DDD)/∑DDTs and o,p′-DDT/p,p′-DDT revealed that the DDTs in the studied area mainly derived from long-term weathering of technical DDTs residue and the input of dicofol.     

Effects of cultivation strategies on the cultivation of Chlorella sp. HQ in photoreactors

Heterotrophic cultivation caused high level of ROS and high lipids accumulation. HMTC is the best culture strategy for improving the microalgal biomass. Chlorella sp. HQ had great nutrient removal capacity under five culture strategies. The effects of cultivation strategies (including autotrophic cultivation (AC), heterotrophic cultivation (HC), fed-batch cultivation (FC), heterotrophic+ autotrophic two-stage cultivation (HATC), and heterotrophic+ mixotrophic two-stage cultivation (HMTC)) on the growth and lipid accumulation of Chlorella sp. HQ and its total nitrogen (TN) and total phosphorus (TP) removal in secondary effluent were investigated in column photoreactors. The results showed that the TN and TP removal rates ranged between 93.72%–95.82% and 92.73%–100%, respectively, under the five different strategies. The microalgal growth potential evaluated by the maximal growth rate (R_max) was in the order of HMTC>HC>FC>AC>HATC. The values of biomass, total lipid yield, triacylglycerols (TAGs) yield, and total lipid content of the microalga cultivated in the last 5 d increased significantly, but the TAGs productivities of the five strategies were lower than those in the first 7 d. Compared with all the other cultivation strategies, the TAGs productivity and yield after 12 d of cultivation under the heterotrophic condition reached the highest values accompanying the highest level of intracellular reactive oxygen species (ROS), in which the TAGs yield reached 40.81 mg/L at the end of the cultivation period. The peaks in TAGs yield and ROS level suggested that HC was beneficial for lipids accumulation via regulating the cellular redox status and exerting ROS stress on microalgal cells. In summary, HMTC was the best cultivation strategy for improving the microalgal biomass and HC was the best strategy for microalgal TAGs accumulation to produce biodiesel.     

Four genes,morphology and ecology: distinguishing a new species of <Emphasis Type="Italic">Acesta</Emphasis> (Mollusca; Bivalvia) from the Gulf of Mexico

There is currently an active scientific debate about the most correct and efficient way to identify species. To date, few studies in the marine realm have combined the available taxonomic methods. In this study we have used morphology, ecology and molecular analyses to identify a new species within the bivalve genus Acesta. All four genes studied (12S, 16S, Cytb, COI) suggested that a common cold-seep species in the Gulf of Mexico, A. bullisi, should be divided into two distinct species. This conclusion was supported by morphological traits and by observations of ecological distribution. A. oophaga Järnegren, Schander and Young n. sp. is described here, and A. bullisi Vokes (Tulane Stud Geol 2:75–92, 1963) is re-described. This study shows that DNA barcoding in combination with traditional morphological and ecological analyses may be an important tools to identify hidden biodiversity among deep-water organisms such as bivalves.     

Zum protonephridialsystem mariner gastrotrichen der ordnung macrodasyoidea

The protonephridia of marine gastrotrichs are described from Paradasys subterraneus Remane, Turbanella cornuta Remane, and three other species of the Turbanellidae. Both genera have several terminal organs in serial distribution. Paradasys has 6, Turbanella 4 groups of protonephridia. In Paradasys, 3 protonephridial tubules form a continuous system, while in Turbanella such a system consists of 2 to 4 (5) separate protonephridial tubules.     

Changes of microbial composition during wastewater reclamation and distribution systems revealed by high-throughput sequencing analyses

This study employed 454-pyrosequencing to investigate microbial and pathogenic communities in two wastewater reclamation and distribution systems. A total of 11972 effective 16S rRNA sequences were acquired from these two reclamation systems, and then designated to relevant taxonomic ranks by using RDP classifier. The Chao index and Shannon diversity index showed that the diversities of microbial communities decreased along wastewater reclamation processes. Proteobacteria was the most dominant phylum in reclaimed water after disinfection, which accounted for 83% and 88% in two systems, respectively. Human opportunistic pathogens, including Clostridium, Escherichia, Shigella, Pseudomonas and Mycobacterium, were selected and enriched by disinfection processes. The total chlorine and nutrients (TOC, NH₃-N and NO₃-N) significantly affected the microbial and pathogenic communities during reclaimed water storage and distribution processes. Our results indicated that the disinfectant-resistant pathogens should be controlled in reclaimed water, since the increases in relative abundances of pathogenic bacteria after disinfection implicate the potential public health associated with reclaimed water.     

Differences in the species- and size-composition of fish assemblages in three distinct seagrass habitats with differing plant and meadow structure

Fish faunas were sampled seasonally using a large and a small beam trawl in three seagrass habitats comprising predominantly Amphibolis griffithii or Posidonia sinuosa or Posidonia coriacea, which differ in seagrass and meadow structure. Amphibolis griffithii and P. sinuosa both produce a relatively dense leaf canopy, but the former exhibits a distinct architecture, with the leaf canopy overlying relatively open spaces surrounding woody stems, compared to the uniformly dense blade-like leaves of P. sinuosa which emerge directly from the sediment. In comparison, P. coriacea provides a landscape of patchy seagrass amongst areas of bare sand. Since the latter seagrass habitat contains large areas of sand, fish were also sampled in adjacent unvegetated areas. The number of species and density of fish were greater (P<0.05) in P. sinuosa than in either A. griffithii or P. coriacea. The mean number of species caught using the large trawl ranged from 16 to 24 in the first of these habitats compared to 14–21 and 9–15 in the last two habitats, respectively, and the mean densities ranged between 78 and 291 fish 1000 m^?2 in P. sinuosa compared to 31–59 fish 1000 m^?2 in A. griffithii and 31–59 fish 1000 m^?2 in P. coriacea. The biomass of fish was greater (P<0.05) in both P. sinuosa and A. griffithii than in P. coriacea (4.2–5.3 kg and 3.3–6.2 kg versus 0.7–1.9 kg 1000 m^?2, respectively). Furthermore, the size-structure of fish differed among these habitats, where the median weight of fish was 72.1 g in A. griffithii, compared to 7.5 g and 19.8 g in P. sinuosa and P. coriacea, respectively. Ordination and ANOSIM demonstrated that the species-composition differed markedly among the three seagrass habitats (P<0.001), suggesting that fish species display a distinct preference for particular seagrasses characterised by different architecture. Differences in species-composition among the seagrass habitats partly reflected the size-composition of fish in each habitat. The open space below the canopy of A. griffthii is likely to allow larger fish to occupy this habitat, whereas only small fish would be able to penetrate the dense foliage of P. sinuosa. Differences in species- and size-composition of fish among these habitats may be the result of settlement-sized larvae discriminating between particular seagrass and meadow structures, or fish being subject to different levels of predation and/or accessibility to food or space. The species-composition in P. coriacea was highly dispersed and did not differ from that of unvegetated areas. While several species were associated with both P. coriacea and bare-sand habitats, some species did display a high affinity with the seagrass P. coriacea. This may reflect an association with the sparse and narrower leaves of this seagrass or with the patchy occurrence of the seagrass Heterozostera tasmanica, which commonly occurs as an understorey in this habitat.     

Arsenic,antimony, and other trace element contamination in a mine tailings affected area and uptake by tolerant plant species

The study was conducted to characterize mineralogical and elemental composition of mine tailings in order to evaluate the environmental hazards, and identify the metal accumulation potential of native plant species from São Domingos mine, one of the long-term activity mines of the Iberian Pyrite Belt dating back to pre-Roman times. The mine tailings including soils and different plant species from São Domingos were analyzed for determination of tailings characteristics and chemical element contents in tailings and plants. The large amounts of mining wastes are causing significant adverse environment impacts due to acid mine drainage production and mobilization of potentially toxic metals and metalloids in residential areas, agricultural fields, downstreams, and rivers. The typical mineralogical composition is as follows: quartz, micas, K-feldspar, olivine-group minerals, magnetite, goethite, hematite, jarosite, and sulfides. The mine tailings were highly contaminated by As, Ag, Cr, Hg, Sn, Sb, Fe, and Zn; and among them, As and Sb, main contaminants, attained the highest concentrations except Fe. Arsenic has exhibited very good correlations with Au, Fe, Sb, Se, and W; and Sb with As, Au, Fe, Se, Sn, and W in tailings. Among the all plant species, the higher concentrations of all the metals were noted in Erica andevalensis, Erica australis, Echium plantagium, and Lavandula luisierra. Considering the tolerant behavior and abundant growth, the plant species Erica australis, Erica andevalensis, Lavandula luisierra, Daphne gnidium, Rumex induratus, Ulex eriocladus, Juncus, and Genista hirsutus are of major importance for the rehabilitation and recovery of degraded São Domingos mining area.     

Seasonal changes in biomass,growth rates and production of subantarctic calanoid copepods in the Bay of Morbihan,Kerguelen Islands

The present study addresses the ecology of two dominant copepod species in the Bay of Morbihan, Kerguelen Archipelago. The biomass of the herbivore Drepanopus pectinatus (from 2 mg m^?3 in winter up to 500 mg m^?3 in summer) is tightly coupled to seasonal changes in chlorophyll a concentration in the region, whereas the biomass of the predatory euchaetiid Paraeuchaeta antarctica increases during two distinct periods over the year: 250 mg m^?3 in early summer, with the recruitment of the annual generation, and 100 mg m^?3 in autumn, with the deposition of lipids as energy reserves in C5 stages and adults. The juvenile growth rates predicted by temperature-dependent models (0.09 day^?1) closely approximate those observed in D. pectinatusin summer, but are much greater than those observed in P. antarctica (from 0.001 to 0.04 day^?1 depending on developmental stages). This difference can be explained by the reproductive strategies and trophic positions of the two species and may also result from the dependence of larval growth on energy reserves in P. antarctica. The production rates are five- and tenfold greater in juvenile stages than in adults, respectively, for D. pectinatus and P. antarctica. The secondary production by D. pectinatusis insufficient to support P. antarcticaduring winter, when the predatory species probably shifts to alternate prey. In summer the predation by P. antarctica accounts for only a minor part of the mortality estimated for D. pectinatus (from 20% to 60% depending on the examined station). At two of the three stations examined in the Bay of Morbihan, the production of P. antarctica could potentially support the dietary requirements of planktivorous seabirds in the region (~2,000 kg prey day^?1 for common diving petrels, Pelecanoides urinatrix, and ~90 kg prey day^?1 for rockhopper penguins, Eudyptes chysocome filholi).     

Source water odor in one reservoir in hot and humid areas of southern China: occurrence,diagnosis and possible mitigation measures

Background

Identifying typical odor-causing compounds is essential for odor problem control in drinking water. In this study, aiming at a major water source reservoir in hot and humid areas in southern China, which encountered seasonable odor problems in recent years, an integrated approach including comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC?×?GC–TOFMS), flavor profile analysis (FPA) and quantitative real-time polymerase chain reaction (qPCR) was adopted to investigate the odor occurrence.

Results

The results indicated that earthy–musty odor is blamed to the seasonable odor problems, and it is consistent with the complaints results from consumers. Fifty-four typical odor compounds were investigated in the reservoir and twelve were detected, of which, 2-methylisoborneol (2-MIB) was significantly increased during the odor event. Pseudanabaena sp. is the dominant species in the reservoir, which can be further represented by the number of mic gene with qPCR method (R²?=?0.746, P?<?0.001). Oxygen consumption (COD_Mn) and dissolved organic carbon (DOC) have great influence on growth of Pseudanabaena sp., and the release of 2-MIB from the Pseudanabaena sp. cells is affected by temperature and light.

Conclusion

Our findings demonstrated that 2-MIB is the odor-caused substance in the reservoir and Pseudanabaena sp. is the main 2-MIB producer, which was confirmed as a benthic filamentous algae. Due to COD_Mn and DOC have great influence on Pseudanabaena sp. growth, further measures to reduce the CODMn and DOC input should be performed. We also demonstrated that the 2-MIB release is affected by temperature and light. The risk of sudden increase of 2-MIB will be reduced by raising the depth of water in the reservoir. Our study will improve the understanding of T&O problems in this city, as well as in other hot and humid area.

     

Hydrologic and water quality performance of a laboratory scale bioretention unit

A bioretention unit (BRU) or cell is a green infrastructure practice that is widely used as a low impact development (LID) technique for urban stormwater management. Bioretention is considered a good fit for use in China’s sponge city construction projects. However, studies on bioretention design, which incorporates site-specific environmental and social-economic conditions in China are still very much needed. In this study, an experimental BRU, consisted of two cells planted with Turf grass and Buxus sinica,was tested with eighteen synthesized storm events. Three levels (high, median, low) of flows and concentrations of pollutants (TN, TP and COD) were fed to the BRU and the performance of which was examined. The results showed that the BRU not only delayed and lowered the peak flows but also removed TN, TP and COD in various ways and to different extents. Under the high, medium and low inflow rate conditions, the outflow peaks were delayed for at least 13 minutes and lowered at least 52%. The two cells stored a maximum of 231 mm and 265 mm for turf grass and Buxus sinica, respectively. For both cells the total depth available for storage was 1,220 mm, including a maximum 110 mm deep ponding area. The largest infiltrate rate was 206 mm/h for both cells with different plants. For the eighteen events, TP and COD were removed at least 60% and 42% by mean concentration, and 65% and 49% by total load, respectively. In the reservoir layer, the efficiency ratio of removal of TN, TP and COD were 52%, 8% and 38%, respectively, within 5 days after runoff events stopped. Furthermore, the engineering implication of the hydrological and water quality performances in sponge city construction projects is discussed.

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Characteristics of residual organochlorine pesticides in soils under different land-use types on a coastal plain of the Yellow River Delta

The residual levels of organochlorine pesticides (OCPs) were examined in soils covering five types of land use along a salinity gradient on the Yellow River Delta. The most prominent OCPs were dichlorodiphenyltrichloroethane (∑DDT, arithmetic mean = 5.11 μg kg^?1), hexachlorocyclohexane (∑HCH, 1.69 μg kg^?1) and ∑endosulfan (10.4 μg kg^?1). The spatial variability of OCPs composition shifted from γ-HCH and o,p′-DDT dominated pesticides in coastal soils to p,p′-DDE dominated pesticides in inland soils. In different land-use types, the percentages of β-HCH and p,p′-DDE are characterized by more recalcitrant components in decreasing order of vegetable fields, cereal fields, cotton fields, wetlands and tidal flats with increasing soil salinity. However, the less recalcitrant components, γ-HCH and o,p′-DDT, showed an opposite trend. Endosulfan sulfate predominated in all land-use types. Residual levels of β-HCH were affected by soil organic matter. The correlations between γ-HCH and clay content and between p,p′-DDE, o,p′-DDT and salinity might associate with the influence of sediment cotransport by the Yellow River and the density of anthropogenic activities in coastal region. Depth distribution of the OCPs in typical soil profiles also implied that local historical usage and sediment transport by the Yellow River both affected the OCPs residual in this region.     

Simple model of sludge thickening process in secondary settlers

In wastewater treatment plants (WWTPs), a secondary settler acts as a clarifier, sludge thickener, and sludge storage tank during peak flows and therefore plays an important role in the performance of the activated sludge process. Sludge thickening occurs in the lower portions of secondary clarifiers during their operation. In this study, by detecting the hindered zone from the complete thickening process of activated sludge, a simple model for the sludge thickening velocity, u _s = aX ^b (a = 0.9925SSVI _3.5, b = 3.541ln(SSVI _3.5)+12.973), describing the potential and performance of activated sludge thickening in the hindered zone was developed. However, sludge thickening in the compression zone was not studied because sludge in the compression zone showed limited thickening. This empirical model was developed using batch settling data obtained from four WWTPs and validated using measured data from a fifth WWTP to better study sludge thickening. To explore different sludge settling and thickening mechanisms, the curves of sludge thickening and sludge settling were compared. Finally, it was found that several factors including temperature, stirring, initial depth, and polymer conditioning can lead to highly concentrated return sludge and biomass in a biologic reactor.     

Population structure of two northern hemisphere polychaetes,<Emphasis Type="Italic"> Neanthes virens</Emphasis> and<Emphasis Type="Italic"> Hediste diversicolor</Emphasis> (Nereididae), with different life-history traits

The present study compared population genetic structure of two northern hemisphere polychaetes, Neanthes virens (Sars, 1835) and Hediste diversicolor (O.F. Müller, 1776), with different life-history traits. N. virens has a pelagic larval phase that may last as long as 9 days, while H. diversicolor broods its offspring. It was predicted that N. virens populations, especially over relatively short geographic distances, would be more genetically similar than H. diversicolor populations. Sequence data were obtained for two mitochondrial genes, cytochrome c oxidase I (COI) and cytochrome b (cyt b). The COI gene showed no variation in 16 N. virens individuals from 12 locations, and it was not examined in H. diversicolor. The nucleotide sequence of the cyt b gene was examined in 93 N. virens individuals collected in 1992, 1999, and 2000 from 12 localities throughout its range (North America, Europe, Japan) and from 33 H. diversicolor individuals collected in 1999 and 2001 from one locality in eastern Canada and two localities in France (Roscoff and Marseille). In N. virens, one cyt b haplotype was shared by 89% (83 out of 93) and only two other haplotypes were found. Significant population structure was observed in H. diversicolor. In the 33 sequences compared, 18.9% of sites were polymorphic and 12 haplotypes were identified. There were two haplotypes in the Canadian population, three in the Marseille samples, and seven in the Roscoff samples, and no haplotype was found in common between any two sites. These results show that widely separated H. diversicolor populations are strongly differentiated at the cyt b locus. The most plausible interpretation for the low variation at the COI and cyt b loci in N. virens, and for the lack of variation at allozyme loci (based on an initial survey of a smaller subset of populations), is that this species has experienced a drastic bottleneck and that a few remaining lineages recolonized its entire range.