Comparative use of lime and Moringa oleifera in removal of suspended solids from coffee processing effluent
In Kenya, coffee grows in only a small part of 20% of the whole country which is arable land. It grows well between 1200 m and 2100 m above sea level and an annual rainfall of more than 1000 mm. Besides that, coffee does well in areas with red roam soil wh ich is deep and self - draining. It is grown by two economic sectors namely the small holder who are in cooperative societies and in small, medium and large estates. It has been identified with occasional environmental pollution threat in particular during the peak season. Such pollution has been attributed to the coffee p rocessing wastes in particular the voluminous effluent . However, the final grading effluent which constitutes the largest component of the e ffluent has been recommended fo r recycling back to the pulping and washing operations . The washing effluent is also preferably mixed with the pulp which can subsequently be composted for agricultural use. Therefore, the pulping effluent remains as the only component in need of serious c oncern. Recent studies found minimization of water used for processing followed by treatment as the most practical solution towards a lleviation of pollution from coffee pulping effluent . One of the postulated forms of treatment targets the removal of the s usp ended solids from t he effluent prior to its discharge to the percolation disposal pits. The first part of this study sought to relate the levels of suspended solids in the effluent to the specific amount of water used for processing the ripe coffee cherry. That was followed by evaluation of t hree options for removing suspended solids from the pulping effluent . The first trial degraded the raw effluent natural ly by allowing it to remain resident un der normal ambient laboratory conditions until no more solids precipitated out of the effluent. During that time the effluent was not disturbe d except possibly slightly during measurements of the relevant parameters The second one involved application of lime at different rates to the effluent immediately af ter pulping . The third option treated the pulping effluent with different rates of dry and finely ground oil press cake from m oringa oleifera seeds. In all these experiments, the pH, total and dissolved solids in the effluent were measured at preset intervals against time. The precipitated suspended solids from the effluent were also measured as well. Other remarkable observations were also made and recorded. Finally comparative seepage tr i a ls were conducted using the raw and treated effluent applied to the conventional percolation pit models. Results of these tr i a ls were such that natural biodegradation caused the removal of solids from an initial concentration of 3 – 9 g/l to less than 2. 0 g/l in 3 – 10 days . In general, between 50 to 90% of the soli ds were removed from the effluent within that period . However, addition of lime to the effluent even at its optimum rate of 2.0 g/l did not improve the rate or extent of the solids removal over the natural settlement. As for m oringa oleifera , its optimum application rate was 1.0 – 2.5 g/l of effluent. Th a t dosage consistently resulted with a distinct precipitation of solids from the effluent in 24 hours after treatment. Since pulping of coffee is a batch process at almost 24 hour intervals, the treatment of effluent with moringa would therefore be the most compatible to the locally practiced conventional coffee processing system. As for the disposal of the effluent, p ercolation of the treated effluent from the pits was 1.66 – 3.75; 3.07 – 6.57 a nd 1.62 – 2.86 times faster than the raw effluent in 3 sites located at Kisii, Koru and Ru iru respectively. Another dimension was that, t he treated effluent had mainly two phases namely a solids free effluent and settled sludge. Occasionally, either some scum formed on the surface or/and some sludge dislodged from the bottom to the surface of the effluent. The sludge if from lime xiv and moringa treatments has enhanced potentia l for economic utilization be sides broadening the value addition options for these flocculants.