Lc Campos

Biomass development in slow sand filters

Microbial biomass development in the sand and schmutzdecke layer was determined in two full-scale slow sand filters, operated with and without a light excluding cover. A standard chloroform fumigation-extraction technique was adapted to routinely measure microbial biomass concentrations in the sand beds. Sand was sampled to a depth of 10 cm and schmutzdecke was also collected at the same random positions on the uncovered filter. Interstitial microbial biomass in the uncovered sand bed increased with time and decreased with sampling depth. There was a small accumulation of sand biomass with time in the covered filter, but no relationship was apparent between biomass concentration and depth in this filter. Schmutzdecke did not develop on the covered filter and was spatially highly variable in the uncovered condition compared to the consistent patterns observed in interstitial biomass production. It is speculated that microbial biomass in the sand of uncovered filters is largely related to carbon inputs from photosynthetic activity in the schmutzdecke and involves mechanisms that spatially distribute carbon substrate from the schmutzdecke to the sand. However, total organic carbon and dissolved organic carbon removals were similar in both filters suggesting that relatively small biomass populations in covered filters are sufficient to remove residual labile carbon during advanced water treatment and little further advantage to water purification and organic carbon removal is gained by the increased production of biomass in uncovered slow sand filter beds.

Combined remediation and lipid production using Chlorella sorokiniana grown on wastewater and exhaust gases

Substitution of conventional feedstock with waste based alternatives is one route towards both remediation and reducing costs associated with production of algal biomass. This work explores whether exhaust gases and wastewater can replace conventional feedstock in the production of biomass from Chlorella sorokiniana. Exhaust gases were used to augment production in final effluent, anaerobic digester centrate or in standard medium. Cultures were grown in 1L bottles under illumination of 80 μmol m(-2) s(-1). The results showed an average μmax ranging between 0.04 and 0.07 h(-1), whilst the final biomass yield in different media ranged between 220 and 330 mg L(-1). Lipid yield was increased over time to 31 mg L(-1). CO2 addition resulted in complete nitrogen removal between 48 and 96 h in both final effluent and centrate. The results also indicated that levels of carbon monoxide, carbon dioxide and nitrogen oxides in the exhaust gases can be reduced by between 20% and 95%.

Breakage and regrowth of Al-humic flocs--effect of additional coagulant dosage.

The growth, breakage and regrowth of flocs formed by aluminum sulfate (alum) with humic acid (HA) in water at neutral pH was investigated by jar testing with continuous optical monitoring. Various initial dosages of alum and different breakage shears were investigated to compare the floc strengths and to explore the growth of flocs and regrowth of broken flocs. In all cases there was significant irreversibility of floc breakage when no additional coagulant was added. On the other hand, when a small additional dosage of alum was added to the suspension during floc breakage, the size of regrown flocs was higher than that before breakage. The result did not change with the variation of the initial dosage of alum, and the intensity and duration of floc breakage, provided that the additional coagulant was added shortly before the end of the breakage process. It seems that aluminum hydroxide is better able to form flocs, when newly precipitated, rather than after an extended period of high shear.

Breakage and re-growth of flocs formed by charge neutralization using alum and polyDADMAC

The formation, breakage and re-growth of flocs were investigated using alum and polyDADMAC to explore the reversibility of floc breakage. There is a significant reversibility of the breakage process, i.e. the broken flocs can re-grow to the size before breakage, when charge neutralization dominates the coagulation mechanism. However, for higher alum dosage, the break-up process displayed a distinct irreversibility. When coagulated in charge neutralization, the re-growth process of alum was nearly the same as that of polyDADMAC. The average size, coagulation rate and fractal dimension of flocs before and after breakage were nearly the same, including alum and polyDADMAC. While at higher alum dosage, the average size, coagulation rate and fractal dimension of flocs after breakage were much lower than that before breakage. Most important is that the number of small flocs after breakage and re-growth was much less than before breakage when charge neutralization dominated the coagulation mechanism. On the contrary, at higher alum dosage, the small flocs, after breakage and re-growth, increased. The fractal dimension of flocs with alum increased as coagulation time increased until a limiting floc size was reached, while for higher alum dosage, it decreased, whether before or after breakage. The determining parameter for floc re-growth is probably not the fractal dimension, but rather the chemical characteristics of the flocs surface.

Breakage and re-growth of flocs: Effect of additional doses of coagulant species

Several polyaluminum chloride (PACl) coagulants were prepared, with different OH/Al ratios (B values), and characterized by Ferron assay. These were used in studies of floc formation, breakage and re-growth with kaolin suspensions under controlled shear conditions, using a continuous optical monitoring method. Particular attention was paid to the effect of small additional coagulant dosages, added during the floc breakage period, on the re-growth of broken flocs. The results showed that the re-growth ability was greatly dependent on the nature of the PACl species added as second coagulant. The re-growth ability of broken flocs was greatest when the second coagulant was PACl(0) (i.e. AlCl(3), with B = 0) and least with PACl(25) (B = 2.5). In the latter case there was no effect on floc re-growth, irrespective of the initial coagulant used. PACls with intermediate B values gave some improvement in floc re-growth, but less than that with PACl(0). Additional dosage of PACl(0) gave re-grown flocs about the same size or even larger than those before breakage. The re-growth of broken flocs is significantly correlated with the species Al(a) (monomeric) and Al(b) (polymeric), as determined by Ferron assay. The amorphous hydroxide precipitate formed from PACl(0), (mainly Al(a)) can greatly improve the adhesion between broken flocs and give complete re-growth. However, for PACl(25), mostly composed of Al(b), the nature of the precipitate is different and there is no effect on floc re-growth.

Photocatalytic degradation of trichloroethylene in aqueous phase using nano-ZNO/Laponite composites

The feasibility of nano-ZnO/Laponite composites (NZLc) as a valid alternative to TiO2 to mineralize trichloroethylene (TCE) without difficulties for recovery of photocatalysts was evaluated. Based on the experimental observations, the removal of TCE using NZLc under UV irradiation was multiple reaction processes (i.e., sorption, photolysis, and photocatalysis). Sorption of TCE was thermodynamically favorable due to the hydrophobic partitioning into crosslinked poly vinyl alcohol, and the adsorption onto high-surface-area mineral surfaces of both ZnO and Laponite. The degradation efficiency of TCE can be significantly improved using NZLc under UV irradiation, indicating that ZnO-mediated heterogeneous photocatalytic degradation occurred. However, the degradation efficiency was found to vary with experimental conditions (e.g., initial concentration of TCE, loading amount of NZLc, the intensity of light and initial solution pH). Although the removal of TCE by NZLc was found to be a complex function of sorption, photolysis, and photocatalysis, the photocatalytic degradation of TCE on the surface of ZnO was critical. Consequently, developed NZLc can be applied as a valid alternative to suspended TiO2 powder, and overcome drawbacks (e.g., filtration and recovery of photocatalysts) in degradation of TCE for various water resources.

Effect of sludge retention on UF membrane fouling: The significance of sludge crystallization and EPS increase

This paper concerns a previously unreported mechanism of membrane ultrafiltration (UF) fouling when a UF process with coagulation pre-treatment is used in drinking water treatment. The significance of settled coagulant solids (sludge) with different age within the membrane tank on UF fouling has been investigated at laboratory-scale, using model micro-polluted surface water. The process of floc crystallization and increasing bacterial EPS with solids (sludge) retention time may be detrimental to UF operation by causing an increased rate of membrane fouling. In this study the performance of two alum pre-treated hollow-fibre UF units, operated in parallel but with different settled sludge retention times (1 and 7 days), was compared. The results showed that over 34 days of operation the extent of reversible and irreversible fouling was much greater for the 7-day solids retention time. This was attributed to the greater extent of bacterial activity and the presence of Al-nanoparticles, arising from sludge crystallization, at the longer retention time. In particular, greater quantities of organic matter, particularly EPS (proteins and polysaccharides), were found in the UF cake layer and pores for the 7-day retention time. The addition of chlorine later in the membrane run substantially reduced the rate of membrane fouling for both sludge retention times, and this corresponded to reduced quantities of organic substances, including EPS, in the cake layer and pores of both membranes. The results suggest that bacterial activity (and EPS production) is more important than the production of Al-nanoparticles from solids crystallization in causing membrane fouling. However, it is likely that both phenomena are interactive and possibly synergistic.

Efficient degradation of sulfamethoxazole by the Fe(II)/HSO5− process enhanced by hydroxylamine: Efficiency and mechanism

Fenton or Fenton-like processes have been regarded as feasible methods to degrade a wide variety of contaminants by generating reactive species, but the efficiency is still challenged by the slow transformation from Fe(III) to Fe(II) and pH. This study employed hydroxylamine (HA) to improve the oxidation efficiency of Fe(II)/HSO5- (Fe(II)/PMS) process, by selecting sulfamethoxazole (SMX) as the target compound. The degradation efficiency and mechanism of SMX by the HA/Fe(II)/PMS process were elucidated for the first time. Compared with Fe(II)/PMS process, the HA/Fe(II)/PMS process showed about 4 times higher degradation efficiency of SMX at pH 3.0. The analysis of steady-state concentration of Fe species indicated that HA enhanced the transformation of Fe(III) to Fe(II), sustaining the rapid Fenton-like reactions. Both sulfate radicals and hydroxyl radicals accounted for the degradation of SMX, with the latter regarded as the dominant reactive species. Degradation intermediates of SMX were further analyzed, and three main transformation pathways were thus proposed. The HA/Fe(II)/PMS process was also effective in the removal of SMX and total organic carbon from real pharmaceutical wastewater. This work would broaden the scope of application of Fenton and Fenton-like processes enhanced by HA in contaminants treatment.

Development and application of a methodology to assess sanitary risks in Maputo, Mozambique

Sanitation-related health risks in low-income urban areas are concentrated in localities in which sanitation facilities and infrastructure are poorly developed and maintained. A simple and systematic approach to quantify these risks can be used to identify vulnerable communities and to support decisions about the types of interventions to mitigate these risks. The methodology described in this paper utilizes local stakeholder knowledge in a participatory process to score sanitation risks, using a framework of indicators that provides a quantitative assessment of the intensity and distribution of risk. The approach considers the extent of hazardous events related to faecal contamination of the environment, the level of local community exposure to this hazard, and vulnerability factors that exacerbate the impacts of infection. The paper describes the development of the methodology and its application in Maputo and outlines how this approach might be used to support the preparation of city sanitation plans. The approach is validated through the use of a conventional household survey, the results of which are compared with those from the community workshops.

Influence of PPCPs on the performance of intermittently operated slow sand filters for household water purification.

Removal of pharmaceuticals and personal care products (PPCPs) from drinking water is usually enhanced by advanced oxidation which is not affordable in low income countries. Slow sand filtration has been found to be capable of removing anti-inflammatory compounds, and its low maintenance costs and easy operation make it an attractive technology for treating drinking water in many parts of the world. In addition, slow sand filters can be used at both large and household scales. The biofilm (i.e. schmutzdecke) developed on the top of the sand and within the upper layers of the sand is acknowledged to be responsible for the water purification. However, it is possible that the PPCPs may affect the schmutzdecke development and microbial community within the filters, and consequently the performance of the filter. This study investigated two household slow sand filters (for water purification) operated intermittently with and without contamination by six PPCPs. Eleven parameters were monitored in the affluent and effluent water, including bacterial species present and schmutzdecke biomass development. Results demonstrated that the household slow sand filter performance was not affected by the 2μgL-1 of PPCPs in the water. There was no significant difference between filters for total coliforms and E. coli removal, but there was considerable difference between sampling times. Biomass considerably increased with the number of filtrations in both filters and there was no significant difference between filter biomass. However, it was found that more bacterial species were present in the period with no contamination than during the contamination period. Bacillus anthracis and Exiguobacterium sp. showed to be resistant to the effects of the PPCPs. These suggest there are effects of PPCPs on bacterial species within the filter. However, the effect of the PPCPs on biomass was not conclusive in this study and needs to be further investigated.