Zero Liquid Discharge: Possible but not always sensible

Dur­ing pro­duc­tion, waste­water is pro­duced in many places. In regions with dis­charge restric­tions, for exam­ple, con­cepts for zero liq­uid dis­charge are there­fore attract­ing the atten­tion of com­pa­nies. From a tech­ni­cal point of view, waste­water-free pro­duc­tion is cer­tain­ly pos­si­ble – but it is only worth­while under cer­tain conditions.
What used to appear incon­ceiv­able is today pos­si­ble: mod­ern tech­nol­o­gy can even make waste­water into drink­ing water again. “The tech­ni­cal pos­si­bil­i­ties have devel­oped enor­mous­ly in the last few years. How­ev­er, this does not mean that every­thing that is pos­si­ble has to be exploit­ed”, says Elmar Bil­lenkamp, expert for Zero Liq­uid Dis­charge at Envi­ro­Chemie. The Ross­dorf com­pa­ny devel­ops and builds tai­lor-made sys­tems for water and waste­water treat­ment for its cus­tomers. “The deci­sive ques­tion in a new sys­tem is always: How far must the treat­ment go?” says Billenkamp.

Availability

In the mean­time, a pro­duc­tion method that is com­plete­ly free of waste­water is tech­ni­cal­ly pos­si­ble; with this method, com­pa­nies do not have to dis­charge any waste­water at all into the sewage sys­tem. Such con­cepts for zero liq­uid dis­charge are in par­tic­u­lar demand in regions with water short­ages, for exam­ple. “In these cas­es, the waste­water is pre-treat­ed using a com­bi­na­tion of dif­fer­ent meth­ods to such an extent that most of it can be recy­cled,” explains Bil­lenkamp. For exam­ple it is used for cool­ing sys­tems, irri­ga­tion or for clean­ing purposes.
In oth­er pro­duc­tion facil­i­ties, on the oth­er hand, it is not pos­si­ble to use the local sewage sys­tem. “There are cas­es in which the quan­ti­ty of waste­water from pro­duc­tion would be too much for the local sys­tem or waters – in oth­er cas­es there is no means at all of dis­charg­ing the waste­water, or dis­charg­ing is lim­it­ed by the local author­i­ties, explains Bil­lenkamp. “Then, of course, alter­na­tive solu­tions for the waste­water must urgent­ly be found.” In such cas­es, for exam­ple, the waste­water is treat­ed in such a way that only sludge and brine remain as residues.

Entrepreneurial decision

In regions in which water is abun­dant and inex­pen­sive and there is a prop­er­ly func­tion­ing sewage sys­tem, on the oth­er hand, zero liq­uid dis­charge does not play any part, as a rule. “Then it is sim­ply not worth­while, in eco­nom­ic terms,” says Bil­lenkamp. “In these regions, how­ev­er, it is pos­si­ble that zero liq­uid dis­charge is not a neces­si­ty on account of local con­di­tions, but is an entre­pre­neur­ial deci­sion.” For exam­ple when com­pa­nies are aim­ing to obtain spe­cial envi­ron­men­tal pro­tec­tion cer­tifi­cates like the Lead­er­ship in Ener­gy and Envi­ron­men­tal Design (LEED) cer­tifi­cate, which awards bonus points for an inno­v­a­tive waste­water treat­ment sys­tem. Oth­er com­pa­nies want to make them­selves inde­pen­dent of offi­cial reg­u­la­tions through waste­water-free pro­duc­tion. “The ini­tial invest­ment and the ongo­ing costs for waste­water tech­nol­o­gy can be planned in the long term. As a rule, charges increase in the course of time – some­times also arbi­trar­i­ly,” explains Billenkamp.

In the beginning is the concept

These exam­ples show how diverse the basic con­di­tions for waste­water treat­ment can be. “This is why we do not offer any stan­dard solu­tions. We devel­op tai­lor-made con­cepts for our cus­tomers; these may also result in zero liq­uid dis­charge – but only if it makes sense,” says Bil­lenkamp. With­in the frame­work of a study, for exam­ple, he is cur­rent­ly exam­in­ing the opti­mum treat­ment of the waste­water pro­duced in three loca­tions by a phar­ma­ceu­ti­cal man­u­fac­tur­er in India. There, this glob­al enter­prise pro­duces med­i­cine cap­sules which con­sist essen­tial­ly of gela­tine, or of cel­lu­lose for the veg­an vari­ant. Depend­ing on the cus­tomers’ wish­es, dif­fer­ent colourants are also added. When the facil­i­ties are cleaned, some of these sub­stances are dis­charged into the waste­water. It thus turns green and con­tains a rel­a­tive­ly high amount of organ­ic mate­ri­als as well as nitro­gen compounds.
“Up to now, after a basic clean­ing, the waste­water was used for irri­ga­tion, as there is no munic­i­pal sewage sys­tem. How­ev­er, because water is scarce at the pro­duc­tion loca­tions, the phar­ma­ceu­ti­cal com­pa­ny would like to opti­mise its water man­age­ment and han­dle it espe­cial­ly sus­tain­ably,” explains Bil­lenkamp. “This is why we are cur­rent­ly exam­in­ing what a con­cept for the recy­cling of treat­ed waste­water could look like, if nec­es­sary going as far as zero liq­uid discharge.”

Analysis on site, experiments in the laboratory

In a first step, Bil­lenkamp, as Envi­ro­Chemie’s expert for zero liq­uid dis­charge, analysed the actu­al con­di­tion of the cur­rent waste­water treat­ment on site in India, deter­mined water flows and took sam­ples. “In pilot tests in our lab­o­ra­to­ry in Ross­dorf, we then devel­oped a method with which we can treat the waste water from the pro­duc­tion stage,” says Bil­lenkamp. In this method, the colour is first elim­i­nat­ed through oxi­da­tion. The sub­se­quent chemo-phys­i­cal and bio­log­i­cal clean­ing process­es remove fur­ther sub­stances. A buffer tank com­pen­sates for quan­ti­ty fluc­tu­a­tions, since more waste­water is pro­duced after cleaning.
“After this treat­ment, the waste­water could actu­al­ly be dis­charged into the sewage sys­tem. Since such a sys­tem does not exist, how­ev­er, we devel­oped a recy­cling con­cept,” stat­ed Bil­lenkamp. In a first step, we exam­ined where treat­ed waste­water could be reused, and in what qual­i­ty. Accord­ing to the analy­sis, some of it can still be used for irri­ga­tion. “How­ev­er, this does not work over the whole year. If it rains a lot dur­ing the mon­soon sea­son, the loca­tions can­not also use treat­ed water for irri­ga­tion,” says Bil­lenkamp. Alter­na­tive­ly, reverse osmo­sis can be used to treat the waste­water fur­ther, so that it is suit­able for the cool­ing tow­ers, among oth­er things. The rest is evap­o­rat­ed. “If the phar­ma­ceu­ti­cal com­pa­ny imple­ments the con­cept in this way, there will be no water at the loca­tions which is not used,” says Billenkamp.

“Zero” does not always mean nought

While in this exam­ple from India zero liq­uid dis­charge real­ly means that no water is left unused, this is by no means always the case. Even if no waste­water is dis­charged, liq­uids that have to be dis­posed of are some­times pro­duced. And even if this is not the case, the solids that were removed from the waste­water are left behind in any case. “The waste­water does not sim­ply van­ish into thin air. This is why part of the con­cept must always be what to do with the resid­ual sub­stances,” says Bil­lenkamp. The best idea is for the com­pa­ny to make the best pos­si­ble use of the left­overs: that even makes a “zero” into a plus.