In this laboratory based study fewer C
In this laboratory-based study, 60% fewer C. parvum oocysts paralleled by 80.3% lower turbidity was obtained following 90 min of sedimentation in wastewater treated with 4 mL L of 5% MO seed extract compared with untreated wastewater. This documented effect of increased sedimentation of oocysts in wastewater following treatment with MO seed extract agrees with the results obtained previously for other microorganisms, i.e. helminth eggs, schistosome cercariae and fecal bacteria (Madsen et al., 1987; Olsen, 1987; Sengupta et al., 2012b). Treatment of different types of turbid water with 4mLL of 5% MO seed extract reduced the helminth egg concentration by 94%–99.5% (Sengupta et al., 2012b). Schistosome cercariae were reduced by 90% in artificial Nile water treated with 200mgL MO seeds extract (Olsen, 1987) (equaling 4mLL of a 5% w/v MO seed extract), while a fecal bacterial reduction of 1–4 log units was obtained from four types of turbid water treated with 200mgL MO seed extract (Madsen et al., 1987) (representing 4mLL of a 5% w/v MO seed extract). Cryptosporidium oocysts are small (4–6μm), have a low specific gravity and are therefore considered unaffected by gravitational settling. Extraction of MO seeds with water releases the active ingredients, the dimeric XL184 with a molecular weight of approx. 13kDa and an iso-electric point of 10–11 (Ndabigengesere et al., 1995). The proteins are water-soluble and positively charged (Ndabigengesere et al., 1995; Broin et al., 2002) and can bind negatively charged particles in the water resulting in floc formation (Ndabigengesere et al., 1995). The net charge of oocysts is negative (Drozd and Schwartzbrod, 1996; Brush et al., 1998) and oocysts can presumably attach to MO seed extract or be incorporated into flocs by binding to the positively charged cationic proteins from MO seed extract. The association with the MO seed extract alters the oocysts “effective” size, changing their settling velocity, which most likely led to the reduced number of oocysts in the supernatant of MO treated wastewater. Nevertheless, in our study 3927±1928 oocysts remained in the 450mL supernatant of treated wastewater following 90min of sedimentation. Because the spiking dose of oocysts was relatively high (6.1×105±6.2×104oocystsL), we first hypothesized that insufficient amounts of the active component of MO seed extract were available to allow complete removal of all oocysts during the formation of flocs. However, the turbidity of the water was reduced significantly and we therefore considered the MO seed extract as fully active. Thus, we studied the effect of treatment with MO seed extract on water containing three lower concentrations of oocysts (100, 1000 or 10,000). Hence, these results did not support our hypothesis, as the percent reduction of oocysts between treated and untreated water was equivalent (81%, 71% and 88%) despite different spiking doses. However, it appears as the percent reduction of oocysts between treated and untreated water was greater in river water (81%, 71% and 88%) than in the wastewater (52%) following 60min of sedimentation. This could be due to the different water types, different initial turbidity (see Table 1) or different oocyst batches, although the oocysts used in both river- and wastewater originated from the same cattle farm. The partial removal of oocysts from the MO treated turbid water might be due to variations in the oocysts wall structure of the sedimented oocysts and the oocysts remaining in the supernatant. For example, the oocyst viability was not assessed and it is possible that the non-sedimented oocysts had a different viability status than the sedimented oocysts. Oocysts of different viability status and morphologically degenerated oocysts have different density (Young and Komisar, 2005) which possibly also alters the oocysts wall structure. However, further studies are needed to assess if MO seed extract works differently on viable from non-variable oocysts.