N.F.Y. Tam

Spatial variation of heavy metals in surface sediments of Hong Kong mangrove swamps.

The degree of heavy metal contamination in the fine-grained (<63 microm) and sand-sized (2 mm-63 microm) fractions of surface sediments in 18 different mangrove swamps (144 random samples) in Hong Kong was examined. Higher concentrations of heavy metals were found in the fine-grained than the sand-sized fractions of the sediment; however, the differences between these two fractions became less significant when the swamp was more contaminated. The principal component analyses show that the 18 mangrove swamps, according to the median concentrations of total heavy metals, were clustered into four groups. The first group included three mangrove swamps in Deep Bay region which are seriously contaminated, with heavy metal concentrations in sediments around 80 microg g(-1) Cu, 240 microg g(-1) Zn, 40 microg g(-1) Cr, 30 microg g(-1) Ni, 3 microg g(-1) Cd and 80 microg g(-1) Pb. The second cluster, made up of another four swamps distributed in different geographical locations (two in Sai Kung district and two in Tolo region), also had elevated levels of Cu, Pb, Ni and Cr in the sediments. Field observation reveals that these seven stands received industrial, livestock and domestic sewage as well as pollution from mariculture activities, suggesting that anthropogenic input is the main source of heavy metal contamination in Hong Kong mangroves. The sediments from other mangrove swamps were relatively uncontaminated.

Comparison of the Levels of Bacterial Diversity in Freshwater, Intertidal Wetland, and Marine Sediments by Using Millions of Illumina Tags

ABSTRACT Sediment, a special realm in aquatic environments, has high microbial diversity. While there are numerous reports about the microbial community in marine sediment, freshwater and intertidal sediment communities have been overlooked. The present study determined millions of Illumina reads for a comparison of bacterial communities in freshwater, intertidal wetland, and marine sediments along Pearl River, China, using a technically consistent approach. Our results show that both taxon richness and evenness were the highest in freshwater sediment, medium in intertidal sediment, and lowest in marine sediment. The high number of sequences allowed the determination of a wide variety of bacterial lineages in all sediments for reliable statistical analyses. Principal component analysis showed that the three types of communities could be well separated from phylum to operational taxonomy unit (OTU) levels, and the OTUs from abundant to rare showed satisfactory resolutions. Statistical analysis (LEfSe) demonstrated that the freshwater sediment was enriched with Acidobacteria, Nitrospira, Verrucomicrobia, Alphaproteobacteria, and Betaproteobacteria. The intertidal sediment had a unique community with diverse primary producers (such as Chloroflexi, Bacillariophyta, Gammaproteobacteria, and Epsilonproteobacteria) as well as saprophytic microbes (such as Actinomycetales, Bacteroidetes, and Firmicutes). The marine sediment had a higher abundance of Gammaproteobacteria and Deltaproteobacteria, which were mainly involved in sulfate reduction in anaerobic conditions. These results are helpful for a systematic understanding of bacterial communities in natural sediment environments.

Contamination of polycyclic aromatic hydrocarbons in surface sediments of mangrove swamps

The concentrations of total polycyclic aromatic hydrocarbons (sigmaPAHs) and 15 individual PAH compounds in 20 surface sediments collected from four mangrove swamps in Hong Kong were analysed. sigmaPAH concentrations ranged from 356 to 11,098 ng g(-1) dry weight with mean and median values of 1992 and 1,142 ng g(-1), respectively. These values were significantly higher than those of marine bottom sediments of Hong Kong harbours, suggesting that more PAHs were accumulated in mangrove surface sediments. The concentrations of sigmaPAHs as well as individual PAH compound varied significantly among mangrove swamps. The swamps heavily polluted by livestock and industrial sewage, such as Ho Chung and Mai Po, had much higher concentrations of total PAHs and individual PAH than the other swamps. The PAH profiles were similar among four mangrove swamps, and were dominated by naphthalene (two-ring PAH), fluorene and phenanthrene (three-ring PAH). The mangrove sediments had higher percentages of low-molecular-weight PAHs. These indicated that PAHs in mangrove sediments might originate from oil or sewage contamination (petrogenic input). Ratio values of specific PAH compounds such as phenanthrene/anthracene and fluoranthene/ pyrene, were calculated to evaluate the possible source of PAH contamination in mangrove sediments. These ratios varied among samples, suggesting that mangrove sediments might have a mixed pattern of pyrolytic and petrogenic inputs of PAHs. Sediments collected from Ho Chung mangrove swamp appeared to be more dominated by pyrolytic input while those from Tolo showed strong petrogenic contamination.

Fate of nitrogen during composting of chicken litter

Chicken litter (a mixture of chicken manure, wood shavings, waste feed, and feathers) was composted in forced-aeration piles to understand the changes and losses of nitrogen (N) during composting. During the composting process, the chemical [different N fractions, organic matter (OM), organic carbon (C), and C:N ratio], physical, and microbial properties of the chicken litter were examined. Cumulative losses and mass balances of N and organic matter were also quantified to determine actual losses during composting. The changes in total N concentration of the chicken litter piles were essentially equal to those of the organic N. The inorganic N concentrations were low, and that organic N was the major nitrogenous constituent. The ammonium (NH(4)(+))-N concentration decreased dramatically during first 35 days of composting. However, the rapid decrease in NH(4)(+)-N during composting did not coincide with a rapid increase in (NO(3)(-)+NO(2)(-))-N concentration. The concentration of (NO(3)(-)+NO(2)(-))-N was very low (<0.5 g kg(-1)) at day 0, and this level remained unchanged during the first 35 days of composting suggesting that N was lost during composting. Losses of N in this composting process were governed mainly by volatilization of ammonia (NH(3)) as the pile temperatures were high and the pH values were above 7. The narrow C:N ratio (<20:1) have also contributed to losses of N in the chicken litter. The OM and total organic C mass decreased with composting time. About 42 kg of the organic C was converted to CO(2). On the other hand, 18 kg was lost during composting. This loss was more than half (59%) of the initial N mass of the piles. Such a finding demonstrates that composting reduced the value of the chicken litter as N fertilizer. However, the composted chicken contained a more humified (stabilized) OM compared with the uncomposted chicken litter, which would enhance its value as a soil conditioner.

Microbial activities during composting of spent pig-manure sawdust litter at different moisture contents

The changes in microbial properties, including total aerobic heterotrophs, O2-consumption rate, ATP content, dehydrogenase activity and microbial biomass C and N of the spent pig-manure sawdust litter were examined during further compositing. The effects of three moisture levels, 50% (pile A), 60% (pile B) and 70% (pile C), on the composting process were also evaluated. Piles A and B had very similar trends of change in temperature and microbial properties during the composting period but pile C was significantly different. Temperatures in the first two piles increased to a peak of 64–69°C by day 4, while that of pile C rose to a lower peak (58°C) on day 7. The high moisture content (about 70%) of pile C led to early cooling of the pile and decreased the production of microbial activity and biomass. Although water was added frequently to maintain the moisture content of each pile, it was difficult in practice to maintain the moisture content of pile C at 70%, since water leaked out from the pile. Therefore, a moisture content of between 50 and 60% can be considered as the optimal moisture level for further composting of the spent litter. In general, the total aerobic heterotrophs, O2 consumption rate and ATP content of all piles increased dramatically during the thermophilic stage of composting, but then decreased slowly and were maintained at lower levels at the end of the composting process. Stability of microbial properties was observed at day 60, indicating that two months is enough to convert spent litter to a mature compost. Temperature was found to be correlated with ATP content, dehydrogenase activity and oxygen consumption rate, and so these parameters could be used to indicate microbial activity and degradation of the spent pig-manure sawdust litter.

Effects of composting on phytotoxicity of spent pig-manure sawdust litter

The phytotoxicity of spent pig-manure sawdust litter (spent litter) was evaluated during further composting. Aqueous extracts of the spent litter were prepared by shaking the sample with water (1:10 w/v), and the toxicity of these extracts was determined on relative seed germination, relative root elongation and germination index (GI, a factor of relative seed germination and relative root elongation). The sensitivity of six plant species, namely Brassica parachinensis (Chinese cabbage), Brassica albogalera (Chinese kale), Allium sativum (onion), Cucumis sativus (cucumber), Amaranthus espinosus (Chinese spinach), and Lycopersicon esculentum (tomato) were compared. The effect of different moisture levels during composting on the phytotoxicity of the spent litter was also examined. Phytotoxicity of the spent litter was only evident during the earlier stage of composting (first 14 days) and, that seed germination and root elongation reached 100% (same as the control) towards the end of the composting. The concentrations of the major inhibitors, water-extractable Cu and Zn, and NH4(+)-N of the spent litter, declined during composting, indicating that these inhibitors were gradually eliminated as composting proceeded. Multiple regression analysis showed that the NH4(+)-N content of the spent litter was the most important chemical factor affecting phytotoxicity of the plant species selected for this study. Relative root elongation and GI were more sensitive indicators of phytotoxicity than seed germination. In the present study, the GIs of all plant species were >80% at day 60, indicating that the spent litter had reached its maturation by day 60. The responses of different plant species to the water-extracts of the spent litter were different. Among the six species, Chinese cabbage and Chinese spinach were the most sensitive species, and tomato and cucumber were the least sensitive species to indicate phytotoxicity of the spent litter. Moisture adjustment during the composting process did not affect the results of the phytotoxicity test.

Effect of algal density on nutrient removal from primary settled wastewater

Laboratory scale batch experiments were employed to examine the effect of initial inoculum sizes of algae on their activities and reduction of nutrients form the primary settled municipal sewage. The microalgae, Chlorella vulgaris, with four initial inoculum sizes, namely ‘superconcentrated’ (1 × 107 cells ml−1) ‘concentrated’ (5 × 106 cells ml−1), ‘medium’ (1 × 106 cells ml−1) and ‘low’ (5 × 105 cells ml−1), were applied to primarily treated sewage. The cell number and chlorophyll content of all algal cultures increased gradually in the first week and the rates of increase were similar in all cultures. During the experimental period, even in the ‘superconcentrated’ cultures, the self-shading problem was not found probably due to good mixing. At the end of the 10 days study, over 90% NH4+ —N and 80% PO43—P were removed from wastewater in all cultures except the ‘low’ one. The residual concentrations of NH4+—N, PO43—P, TKN and total P in wastewater were negatively correlated with the cell numbers and chlorophyll content of the cultures. These results indicated that the efficiency of reducing wastewater-borne nutrients by an algal system was directly related to the physiological activity and growth of the Chlorella cells which in turn were affected by the initial inoculum size. The super-concentrated culture with an initial algal density of 1 × 107 cells ml1 seemed to be more beneficial as this treatment achieved satisfactory nutrient removal within 7 days instead of 10. The sharp initial reduction of COD (>50%) and total organic-N (>60%) was not related to the algal number or chlorophyll content, the performance in the control (without algal cells) was similar to that of the algal cultures. This suggests that the removal of COD and TON was mainly due to the metabolism of the indigenous bacteria. Under the open system, the interaction between algal and bacterial cells was significant which could enhance the simultaneous removal of N, P and organic matter from primary settled sewage.

Elimination of phytotoxicity during co-composting of spent pig-manure sawdust litter and pig sludge

Abstract A plant seed germination technique was used to assess the phytotoxicity of spent pig litter-sludge at different stages of composting in forced-aerated piles on the relative seed germination, relative root elongation, and germination index (GI, a factor of relative seed germination and relative root elongation) of Chinese cabbage (Brassica parachinensis) and Chinese spinach (Amaranthus espinosus). The relative seed germination and root elongation of the two plants were significantly retarded by the spent litter-sludge extracts at day 0, but their values increased as composting progressed. From day 49 onwards, their values were similar to that of the control (deionized water) (between 80 and 100%). Increases in both relative seed germination and root elongation of the two plants corresponded with decreases in the concentrations of NH+4-N, water-extractable Cu and Zn of the compost demonstrating that these chemical compounds were gradually eliminated during composting. The multiple regression analyses showed that the NH+4-N and water-extractable Cu concentrations in the spent litter-sludge extracts were the most important chemical factors causing the phytotoxicity. Composting at the top of the forced-aerated pile was slower than the middle, bottom and surface of the pile during the first 49 days of composting. However, from day 49 onwards, there was no difference among the four locations of the spent litter-sludge pile in terms of both plant responses and chemical parameters. These suggest that the spatial variations in the forced-aerated piles, in terms of phytotoxicity, gradually disappeared as the spent litter-sludge became mature.

Microbial Population Dynamics and Enzyme Activities During Composting

The changes in population size of different microbial groups (total aerobic heterotrophs, actinomycetes, fungi, fecal coliforms, ammonium- and nitrite-oxidizing bacteria, and denitrifying bacteria) and the activities of 19 different enzymes (three phosphatases, three esterases, two proteases, three amino-peptidases, and eight glycosyl-hydrolases) were examined during cocomposting of poultry litter (a mixture of poultry manure, waste feed, feathers, and wood shavings) and yard trimmings (a mixture of grass clippings, leaves, and wood barks). Three piles with forced aeration were established by mixing 2:1 (v/v) ratio of poultry litter and yard trimmings. During composting, samples were taken at three different locations (top, middle, and bottom) of the forced aeration piles for microbial and enzyme analyses. Results demonstrated that population size of different microbial groups was not a limiting factor in this composting process as the microorganisms in the poultry litter + yard trimmings compost are in great abundance. Although the numbers of these microbial groups were reduced by high temperature, their populations multiplied rapidly as composting progressed. Fecal coliforms were eliminated by day 49, suggesting that the poultry litter + yard trimmings compost showed an overall increase in diversity and relative abundance of extracellular enzymes present as composting progressed. The population of fungi and actinomycetes (microorganisms active in degradation of cellulose, hemicellulose, and lignin) were positively correlated with esterase, valine amino-peptidase, α-galactosidase, β-glucosidase, and lipase. Of all 19 enzymes examined, ß-galactosidase (enzyme involved in the hydrolysis of lactose) had the most significant positive correlation with microbial populations, such as total aerobic heterotrophs, ammonium- and nitrite-oxidizing bacteria, denitrifying bacteria, and fecal coliforms. Cystine amino peptidase, chymotrypsin, and trypsin showed no evidence of activity during the entire period of composting. This composting process represented a combined activity of a wide succession of environments in the compost pile as one microbial group/enzyme overlapped the other and each emerged gradually as a result of the continual change in temperature as well as moisture content, O2 and CO2 level, and progressive breakdown of complex compounds to simpler ones.

Effect of immobilized microalgal bead concentrations on wastewater nutrient removal

A unicellular green microalga, Chlorella vulgaris, entrapped in calcium alginate as algal beads were employed to remove nutrients (N and P) from simulated settled domestic wastewater. A significantly higher nutrient reduction was found in bioreactors containing algal beads (at concentrations ranging from 4 to 20 beads ml(-1) wastewater) than the blank alginate beads (without algae). A complete removal of NH(4)(+)-N and around 95% reduction of PO(4)(3-)-P was achieved within 24 h of treatment in bioreactors having the optimal algal bead concentration (12 beads ml(-1), equivalent to 1:3 algal beads:wastewater, v/v). The NH(4)(+)-N removal was significantly lower at low (around 4 beads ml(-1)) and high (>15 beads ml(-1)) algal bead concentrations. On the other hand, the effect of bead concentration on phosphate removal was less obvious, and bead concentrations ranging from 8 to 20 beads ml(-1) showed comparable percentages of phosphate reduction. Algal uptake and adsorption on alginate gels were found to be the major processes involved in the removal of N and phosphate in the present study. In addition, NH(4)(+)-N could be lost via ammonia volatilization while PO(4)(3-)-P was removed by chemical precipitation, as alkaline pH was recorded in the immobilized microalgal treatment system.