The use of organic watses to reclaim colliery spoils

SIGLELD:D46475/83 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

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 NH4/+-N and around 95% reduction of PO4/3--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 NH4/+-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, NH4/+-N could be lost via ammonia volatilization while PO4/3--P was removed by chemical precipitation, as alkaline pH was recorded in the immobilized microalgal treatment system

Mangrove soils in removing pollutants from municipal wastewater of different salinities

Soil leaching experiments were conducted to assess the capacity of mangrove soils in purifying synthetic wastewater containing pollutant concentrations four times of that found in local municipal sewage and of two salinities (fresh vs. saline water). Results on leachate nutrient and heavy metal concentrations reveal that the mangrove soils were capable of removing certain amount of pollutants from wastewater, and the removal efficiency varied between pollutants. The soils were most effective in retaining heavy metals such as Cu but were less effective for Mn and Zn. Similarly, the wastewater-borne NH4/+ was more easily leached than P. The soil data show that most pollutants were accumulated in the top layer (0-1.5 cm) of the soil tray, with little downward migration. Differences between treated and control soil nutrient and heavy metal concentrations were not found in the soil masses below the surface 1.5 cm. In the surface layer, the mangrove soils treated with wastewater had significantly higher concentrations of NH4/+- N, total and extractable P, total and extractable Cu, Cd, Zn and Mn. On the other hand, there was no significant elevation in total nitrogen content in mangrove soils treated with wastewater when compared with the control. Soils receiving wastewater prepared in deionized water (fresh) had slightly higher pollutant concentrations, and larger enrichment factors than that treated with saline wastewater (containing 1.5% salinity). These results suggest that mangrove soils could retain pollutants from wastewater but its efficiency would slightly be affected by salinity

The comparison of growth and nutrient removal efficiency of chlorella pyrenoidosa in settled and activated sewages

The microscopic green alga, Chorella pyrenoidosa was grown in settled and activated sewage under two different culture systems, batch and semi-continuous. Good growth was obtained in both types of wastewater and the algal production was comparable to and even higher than that found in commerical Bristol medium. The semi-continous culture supported more growth than the batch system. The was a close relationship between algal growth and the amount of nutrient removed from both settled and activated sewage. A more rapid drop in NH4+-N was found in settled rather than activated sewage. The NH4+-N of settled sewage dropped from its initial 27 to 5 mg litre-1 in both culture systems. On the other hand, the NO3- N of activated sewage started to decrease from Day 2 onwards and the final NO3- N concentration was less than 1 mg litre-1 (over 90% removal efficiency). The amount of total inorganic nitrogen being reduced due to algal culture was similar in both types of sewage. The changes of phosphate content followed the same trend in both sewages, the P concentration increased slightly in the first two days then decreased, especially in the semi-continuous cultures. The final ortho-P in the sewages treated by Chlorella in semi-continuous culture was less than 5 mg liter-1 (about 62% reduction). Such removal efficiency was slightly lower than those reported in previous studies. In general, the semi-continuous algal culture appeared to be a more suitable and efficient way for wastewater treatment than the batch system. With respect to the total reduction of wastewater inorganic N and P by means of Chlorella cells, there was no significant difference between settled and activated sewage